@klXXdpag
Perhaps you have moved on in the last year, but here's a solution for others in the same situation. Yes it is simple, no it does require time. Definitely isn't for a home-user that's happy with the in-browser Settings dialog box. I will describe it broadly, you'd have to lookup the details.
Basically, be aware that there are 3 ways to "admin" Chromium-based browsers. Via GPO centrally, via registry locally, and via JSON locally for a stand-alone install. Your "corporate Chrome" uses one of the first 2, your requirement as a non-admin user can be satisfied by the 3rd option.
Steps:
Prepare the policies to your liking. Download the Google Chrome MSI and ADMX admin-policy template. Import the policy files on a test PC, play around in the GPedit.msc to set policies, see which settings you want, maybe some settings are deprecated and you need to pick an alternative, maybe you want to force-install a few extensions on first run. When it is all just right, test it on Vivaldi by changing the RegistryPath to HKLM\SOFTWARE\Policies\Vivaldi. I mean, export the Chrome policies, edit REG file, import as Vivaldi policies. This is the step that OP has probably done already on his home PC.
Convert those registry policies to a JSON file. In Vivaldi address bar, type chrome://policy which will promptly redirect to vivaldi://policy. Click the "Export to JSON" button, and save the file, maybe open in Notepad and clean it up if you like.
Place the file to apply policies. Take the prefs-JSON file you created/cleaned in step2 above, rename it to master_preferences without a file-extension. Place it in the same folder as vivaldi.exe. For example, you may have a portable/stand-alone install where the EXE is located at D:\Apps\Vivaldi\Application\vivaldi.exe. The policy file would sit right next to the EXE, at D:\Apps\Vivaldi\Application\master_preferences.
Testing first. I repeat, test all this at home if you can. If not the trust certificate, try applying some other settings/policy in this method. Delete the Vivaldi policies that you imported into HKLM registry in step1, restart, verify that the expected settings are definitely being applied from the JSON file. If something isn't right, you'd rather catch it at home (preferably in a VM) than waste time and pull your hair out at work.
Having said that, I confirm that this method does work with Vivaldi/Opera/ChrEdge/Chromium. Obviously, my pick of the lot is Vivaldi. It's just a shame that the old Opera engine (my beloved!!!) was junked, and then the new Opera went to pot... The only real alternative left is Firefox and THAT is a different can of worms.
Caution: If you are force-installing an extension on Opera/ChrEdge, it has to be from, and exist on that browser's own Extension-Store. No matter whether you are doing so using GPO/reg/json.
If it helps, know that it has taken you longer to read and comprehend all this, than it will take to actually do it.
For the curious, in the address bar go to about:about in Chrome/Chromium to see a full list of internal settings/diagnostics pages that you can lookup in all Chrome-based browsers (including Vivaldi).
