Fennec F-Droid gained some awareness among people who care about freedom. It’s mentioned in variuos articles, discussed in forums, etc. It has a positive image overall.
Firefox for Android, on the other hand, is believed to be slow and laggy, so Mozilla gave a GeckoView-based version a new name and advertises it as “all new” (remember Quantum? same tactic).
I think we should stick with the Fennec name, so that those who read an old article could come to F-Droid and install it. Don’t make people think WTF is Fenix, how it’s related to Fennec and why the latter is gone.