If you find yourself in a "only Internet Explorer 5.5 is supported" situation, you could perhaps use Ungoogled Chromium and manually install Ublock Origin to buy yourself time to get out of that dead lock.
open -b com.google.Chrome --new --args --disable-features=ExtensionManifestV2Unsupported,ExtensionManifestV2Disabled
When Google finally nerfs that, it is past time to move to Firefox or Brave, the latter of which has explicitly announced uMatrix support.I miss uMatrix, too. Thank you for working on this!
Use Firefox, uBO works great. While I really enjoy seeing people find creative technical workarounds, the reason for it being needed in the first place is Googles fight against Adblockers with Manifest V3. Firefox allows people to sidestep this artificial downgrade of adblocking capabilities.