Its nice they help an addon or two, but does not help if they neglect the overall addon API & don't even let you install other addons not on their cherry picked list, even if they would work just fine!
What are you talking about? When I go to the store on Firefox for Android right now, it shows me a list of 11 "featured" extensions (so 9 is already wrong). To test whether that list is exhaustive, I searched for an extension not in the list (Old Reddit Redirect). I successfully installed it and confirmed that it works. So as far as I can see, both of your claims are completely wrong.
They are rolling the update in vawes abd not all countries are yet affected. But you can still try Fenix based Firefox by installing the Beta ir Nigtly versions
Fenix uses a whitelist-only model for extensions, and had only around 9, last I checked. Based on some github issue comments, it seems like they'd prefer to stay with a whitelist approach for the foreseeable future.
If your extensions are important to you, you'll need to disable auto-updates for Firefox in the Play store, and avoid using 'update all' and similar - that is, if your extensions aren't on the list.
A version of the old app is available through F-Droid, but it purports to de-mozilla-fy the browser, so I presume sync and other things may not work the same.
A couple more info points - yep, they indeed have a list of addons and if the addon is not on the list, you just can't run it, full stop. Even if no one actually tried if it is broken.
I know this as a fact as someone posted a patched build with a custom list covering many more addons. I installed that and tried two addons from that list I use on desktop Firefox. One did not work (ImTranslator), but the other run just fine (Furiganaize) as on desktop. So Firefox developpers are blocking user from using perfectly working addons as they can't be bothered to add them to their fancy list of allowed addons.
About Fennec from F-Droid
I have been using it since Mozilla broke the perfectly working Firefox install on my Android tablet with the quarter baked Fenic based release and so far I have not found anything missing even if it is supposedly cleaned up from non-free parts. But I don't use Firefox sync, so I can't comment on that.
BTW, Fenix based Firefox build is being worked on for F-Droid as well (they had to cut out all the non-free stuff Mozilla puts into a normal Firefox binary, reportedly a lot more than for Fennec) so if Fenix becomes usable one day, one can get it from a source that will not stealthily replace it by something broken.