While only the Discourse team can provide definitive answers about their culture, I have to say, that’s not the impression I get. It seems that effectively, all major browsers are supported as long as they are supported by their developer/provider. And that seems like a reasonable and balanced approach given that overall, the web tends to move fast.
There is probably be a bit of a gray area regarding Firefox ESR 115 with it’s extended maintenance period until August, but I’m not sure how much that would help people who have users on out-of-maintenance operation systems.
So it sounds like the “real solution” would be either an LTS/ESR version of Discourse or a “maximum compatibility” version with less requirements. Which makes me - and that’s mainly why I comment - a bit worried how much development capacity it would eat up that can then not be used to develop new features and make sure that Discourse continues to evolve with the rest of the web (because I feel that is one of the reasons why Discourse has stopped the steady decline of forums, at least to a certain extent).