... No, they don't ; Discourse are serving a browser-feature detection script (believe it or not, this is actually the recommended way to probe a browser engine, rather than blindly block it based on its UA string) and they're looking for these features:
https://arkshine.github.io/discourse-features-test/
(NB: Their announcement was recently edited to also cover "import maps" (Cr89+, Fx108+))
In a nutshell, they're dropping support for Win7/8.1 , where the last Cr and Fx supported versions are 109 and 115esr, respectively...
... Please do ; the posted custom filter blocks Discourse's browser-checking script, so your browser (FxESR-115) will be served the full-blown variant of the Discourse-based forum of interest; please be aware that while this hack currently works, it's not future proof; in, say, 6 months' time, one of the browser features they're checking for might end up in production, hence one (or more) forum function might break, to some extent ...
That's the way to go , though it doesn't offer any additional clue as to why all but one of your existing logins were mysteriously removed ...
Glad to know and... you're welcome ... Saluti !