Maybe Windows under-reports

I check this in internal Vivaldi Task Manager (Shift+Esc)

On my work PC (Windows 11) after a fresh start, the Background page shows ~100MB and 0.0 CPU, though the memory seems to be dropping. ~75MB now. I don't have nearly as much running though, just a single additional process grouped with the Background Page process.

On my personal PC there's 6 additional "App: Vivaldi" processes and the 1 "App: Mail" process aggregated with it. So maybe it's a misbehaving extension? But those seem to have their own processes too. I wish I had some additional insight into what those processes are, but they don't even list a Process ID, so I have nothing to go on.

Oh, maybe that's each window? Yep, closed a window and one of the processes disappeared. Hmmm, CPU dropped from 90±15% to about 25-30%. The window I closed had almost nothing but hibernated tabs, just one active Amazon tab at the time, but that shouldn't have affected the background process, right?

Restoring the window also restored that excess CPU usage. Oh, I don't have Workspaces enabled btw, not sure if that affects anything, but I saw it mentioned under restore Last session.

I've closed all windows, pinned tabs, and this tab for this post is the only tab remaining, but CPU usage is still 3-5% and memory is around 315MB. I've also turned of restore Last session, so I'll update after restarting Vivaldi if that finally cleared things up.

Edit: So memory is down around 200MB (and dropping, seems to settle around 180), but CPU is 4-8%.

Today it's up around 80%±20%. Ran updates this morning, so it's been recently restarted as well.

It's actually down to ~20%.

Should be lower, around 6 to 10 % under normal circumstances.
Really weird on your PC.

Edit: I should point out that I had been moving the windows back with each test and it never had such a significant impact.

I would love for the background process to be lower, but I can survive when the frame rate isn't like 5. (Hopefully hardware acceleration won't cause problems on other devices.)

It would be cool if I could see a trend line for metrics in the Task manager, because I think it's closer to 80% on average, with peaks up to 120% and valleys down to 65%.

But it would probably be more valuable to de-aggregate all the "App: Vivaldi" tasks so issues could be narrowed down, because Mail gets lumped in there too.

So be patient and wait for an other usee who can test more with KDE 6.x.

Second report:

Graphics Feature Status

• Canvas: Hardware accelerated
• Canvas out-of-process rasterization: Enabled
• Direct Rendering Display Compositor: Disabled
• Compositing: Hardware accelerated
• Multiple Raster Threads: Enabled
• OpenGL: Enabled
• Rasterization: Hardware accelerated
• Raw Draw: Disabled
• Skia Graphite: Disabled
• Video Decode: Hardware accelerated
• Video Encode: Software only. Hardware acceleration disabled
• Vulkan: Disabled
• WebGL: Hardware accelerated
• WebGL2: Hardware accelerated
• WebGPU: Disabled
• WebNN: Disabled

Driver Bug Workarounds

• clear_pixel_unpack_buffer_before_copyteximage
• disable_post_sub_buffers_for_onscreen_surfaces
• disable_software_to_accelerated_canvas_upgrade
• enable_webgl_timer_query_extensions
• exit_on_context_lost
• force_cube_map_positive_x_allocation
• force_int_or_srgb_cube_texture_complete
• disabled_extension_GL_KHR_blend_equation_advanced
• disabled_extension_GL_KHR_blend_equation_advanced_coherent
• disabled_extension_GL_MESA_framebuffer_flip_y

Problems Detected

• WebGPU has been disabled via blocklist or the command line.
  Disabled Features: webgpu

• Accelerated video encode has been disabled, either via blocklist, about:flags or the command line.
  Disabled Features: video_encode

• Linux ATI drivers crash on binding incomplete cube map texture to FBO:
  (http://crbug.com/518889)
  Applied Workarounds: force_cube_map_positive_x_allocation

• Disable partial swaps on Mesa drivers (detected with GL_VERSION):
  (http://crbug.com/339493)
  Applied Workarounds: disable_post_sub_buffers_for_onscreen_surfaces

• Disable KHR_blend_equation_advanced until cc shaders are updated:
  (http://crbug.com/661715)
  Applied Workarounds: disable(GL_KHR_blend_equation_advanced),
  disable(GL_KHR_blend_equation_advanced_coherent)

• Software to Accelerated canvas update breaks Linux AMD:
  (http://crbug.com/710029)
  Applied Workarounds: disable_software_to_accelerated_canvas_upgrade

• Force integer or srgb cube map texture complete on Linux AMD:
  (http://crbug.com/712117)
  Applied Workarounds: force_int_or_srgb_cube_texture_complete

• Expose WebGL's disjoint_timer_query extensions on platforms with site isolation:
  (http://crbug.com/808744), (http://crbug.com/870491)
  Applied Workarounds: enable_webgl_timer_query_extensions

• AMD Linux driver crashes when copyTexImage2D is called with PIXEL_UNPACK_BUFFER set to an uninitialized buffer:
  (http://crbug.com/859998)
  Applied Workarounds: clear_pixel_unpack_buffer_before_copyteximage

• Some drivers can't recover after OUT_OF_MEM and context lost:
  (http://crbug.com/893177)
  Applied Workarounds: exit_on_context_lost

• Disable GL_MESA_framebuffer_flip_y for desktop GL:
  (http://crbug.com/964010)
  Applied Workarounds: disable(GL_MESA_framebuffer_flip_y)

I have an AMD Ryzen 3900x and Radeon 6800XT on Wayland (X11 seems to behave the same). 32 GB RAM
KDE Plasma 6.0.5
KDE Framework 6.4.0
Qt 6.7.2
Kernel 6.9.12-1-MANJARO

Disabling Mail, Calendar, and Feeds made no difference. Rebuilding Mail database did nothing to the usage after it was complete.

I have hardware acceleration disabled because for some reason that flag syncs (which is insane because not all systems are the same and that should absolutely be profile/hardware specific, not a syncable flag). But I'll try switching that on to see if it makes a difference.

Pre-hardware acceleration enabled report:

Graphics Feature Status

• Canvas: Software only, hardware acceleration unavailable
• Canvas out-of-process rasterization: Disabled
• Direct Rendering Display Compositor: Disabled
• Compositing: Software only. Hardware acceleration disabled
• Multiple Raster Threads: Enabled
• OpenGL: Disabled
• Rasterization: Software only. Hardware acceleration disabled
• Raw Draw: Disabled
• Skia Graphite: Disabled
• Video Decode: Software only. Hardware acceleration disabled
• Video Encode: Software only. Hardware acceleration disabled
• Vulkan: Disabled
• WebGL: Software only, hardware acceleration unavailable
• WebGL2: Software only, hardware acceleration unavailable
• WebGPU: Disabled
• WebNN: Disabled

Problems Detected

• WebGPU has been disabled via blocklist or the command line.
  Disabled Features: webgpu

• WebGL2 has been disabled via blocklist or the command line.
  Disabled Features: webgl2

• Accelerated rasterization has been disabled, either via blocklist, about:flags or the command line.
  Disabled Features: rasterization

• Accelerated video encode has been disabled, either via blocklist, about:flags or the command line.
  Disabled Features: video_encode

• Accelerated video decode has been disabled, either via blocklist, about:flags or the command line.
  Disabled Features: video_decode

• WebGL has been disabled via blocklist or the command line.
  Disabled Features: webgl

• Gpu compositing has been disabled, either via blocklist, about:flags or the command line. The browser will fall back to software compositing and hardware acceleration will be unavailable.
  Disabled Features: gpu_compositing

• Accelerated 2D canvas is unavailable: either disabled via blocklist or the command line.
  Disabled Features: 2d_canvas

(1) about mail search database: I don't have any mail configured in Vivaldi

(2) about Use of Hardware Acceleration active: Yes, it is active

(3) about vivaldi://gpu
Graphics Feature Status

• Canvas: Hardware accelerated
• Canvas out-of-process rasterization: Enabled
• Direct Rendering Display Compositor: Disabled
• Compositing: Hardware accelerated
• Multiple Raster Threads: Enabled
• OpenGL: Enabled
• Rasterization: Hardware accelerated
• Raw Draw: Disabled
• Skia Graphite: Disabled
• Video Decode: Hardware accelerated
• Video Encode: Software only. Hardware acceleration disabled
• Vulkan: Disabled
• WebGL: Hardware accelerated
• WebGL2: Hardware accelerated
• WebGPU: Disabled
• WebNN: Disabled

Do you have Settings → Webpages → Use of Hardware Acceleration active?
Can you post content of section Graphics Feature Status of page vivaldi://gpu here?

Deleted all feeds.
Restarted Vivaldi without extensions.

Result:
As soon as I enter a feed (any feed - this time I tried BBC News feed) Background Page process shoots from 0 to 100% CPU.

I guess I'll have to do without feeds on Vivaldi.

Thanks for your time and effort, much appreciated.

Check CPU usage now
If it is low, try a re-import of feeds
Menu File → Import from files and apps → Select Feeds (OPML) file
Select the previously saved OPML file and import

Does that help?