You are right, according to this [1] Fennec is discontinued in favor of Fenix! I only use it for very simple stuff (HN, selfhosted apps etc.), so I did not notice. Yet, looking at the F-Droid store [2], Fennec indeed is available in a recent version (109.2.0) and it is being bumped by Mozilla [3].
Thanks for the clarification! This is what I suspected, too. What matters to me is that it works with custom extension lists. I am not sure I understood what was special about the original "2020 Fennec".
There's also a note from someone on Reddit [1]:
> Fennec is also F-Droid's firefox version. It differs from official ones by having proprietary bits and all telemetry removed as well as unlocked about:config at the moment.
Are you using a recent version of F-Droid fennec (which may be fenix instead), and if so does this one support arbitrary plugins? Did F-droid manage to modify it for that?