Feed detection for other services
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Some services serve RSS and/or Atom feeds but don't announce them properly so these are not detected by Vivaldi now, I know of Vimeo and BitChute (and of course YouTube shenanigans, but you worked this around already it seems), and some WordPress blogs may not have feeds exposed in layout but still serve them so it may be worth trying anyway if you detect that too
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I have found several by simple Search:
SiteName +RSS
or
Sitename +FeedI use Bing Search but your faourite search engine should be able find what you need as some feeds seem to be handled by third party feeders.
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