Everyone using Chromium as base committed to MV2 support, but that's while Chromium itself still supports MV2. What will happen when Google changes things enough that the small browsers can't merge updates in a day or two while maintaining MV2 support? I doubt Vivaldi and Brave have the resources to actually fork Chromium... not even going to mention small projects like Thorium or Ungoogle Chromium.
And the Firefox-based browsers are in a similar position. The 2 or 3 students working on Floorp can't do much if Mozilla decides to drop support and then introduces changes that breaks compatibility with old code.
Of course those browsers can decide to stop merging upstream code, but then you get a Pale Moon... even if we ignore security flaws (which are a problem for you and your machine), a visit to their forum tells me that it struggles with a few websites.
Here is a list of great browsers committed to MV2 support. If anybody from Google tries to gaslight you with "but security..." review this:
https://www.ssllabs.com/ssltest/analyze.html?d=gmail.com
and ask them why do they still support connection with so many insecure tls suites ;-)
Firefox: https://www.mozilla.org/en-US/firefox/new/
Vivaldi: https://vivaldi.com/download/
Brave: https://brave.com/download/
Waterfox: https://www.waterfox.net/download/
LibreWolf: https://librewolf.net/installation/
Pale Moon: https://www.palemoon.org/download.shtml
Thorium: https://thorium.rocks/
Ungoogled Chromium: https://ungoogled-software.github.io/ungoogled-chromium-bina...
Floorp: https://floorp.app/en-US/download