Followed an original developer of FreeTube "PrestonN" through github and he recommends a different extension if you wish for more "official" support. This one did work while I had it installed but I feel safer with the endorsed extension.

For me, with Linux Mint 20.3 and Freetube (flatpak) v. 0.17, this does actually work but not quite as expected. Needs to be refined. Double click is required to open youtube.com links. Other methods of opening youtube.com links open such as "open in new tab" operate as usual and not in freetube.

Consider using the context menu like many other addons; perhaps an option to open in new invidious tab, and fix the double click issue and general unreliability of the addon.

It opens the Freetube app, but not to the video.