I left indeed the boat, but Sailbook still works for now. I also got the new UI on desktop, but in Sailbook I used some nasty tricks to trick Facebook that Sailbook runs on really old devices and requires the old UI. Not sure how long it will last though
I tested Sailbook, the Facebook Mobile App, Firefox, Opera Mini, Sailfish browser, all bring the error. Solution for me was to install Disa messenger that allows you to write Facebook messages. It seems that the Disa framework is opensource. I will use that for the moment, as long as the other solutions are not usable
This is possibly also to do with WhatsApp, which Facebook has been a bit more firm about the “privacy” policy on lately. No telling. A shame to see Sailbook likely won’t work for 2021 unless someone’s willing to maintain it.
For me is solution this: Angelfish -> from bottom right menu set Show desktop site -> go to facebook.com (redirect you to mobile version) -> login to facebook -> go to facebook.com/messages
and you get messages in new responsive desktop webpage. Usable in landscape mode and maybe you also want to hide bottom bar (set from same menu as Show desktop site). It is not as good as native app or Sailbook but better than nothing.