I think the definition of "support" is also important here, it's not like the user-level downloads or modder-level mavens get taken down (i've been rather loud in the past when they were), there's still people like myself working on 1.7.10 and 1.12 projects despite the unsupported nature, and it's functional, which is sufficient enough imo.
There's no tech support on older versions, granted, but honestly there's better places for that anyway, and if you're going to be modding long enough, eventually you'll have to get used to sifting through the decompiled source and making up your own answers anyway.
supporting 1.18 vs 1.19.2, i think it's better to look at things as they are now, and as they have been historically, again as Lex said, none of us have a magic crystal ball, so the best we have to go on is history, since it likes to repeat because humanity doesn't learn.
The greatest examples being during the 1.12.2 releases or the 1.7.10 release, both on the heels of a user-level identical release that few really paid attention to (1.12.0 and 1.7.2), with more active communities a little further back (1.11 and 1.6.4), more likely than not I anticipate this would be more of the same, and since forge is more aimed at chasing the latest as Lex states, latest will always be the real focus, so the secondary one should probably be the one that's older, since it would be easier to cover with more people knowing answers questions, and having more questions already answered in existing posts, otherwise both forge and mod devs are chasing two perpetually moving targets, especially in the case of new projects that are absolutely massive like Create was at one point, having all that work starting from scratch in addition to having to constantly chase every time mojank farts is unreasonable which is why mod devs will stay on a major version until they feel their main goals are reached. That's not to say forge doesn't have similar troubles itself, but more-so to amplify there's a shared issue.
The skeptic in me would say a simpler solution long-run would be having API level access structures, rather than relying on mojank's direct structure since they can't just stick with one way to do literally anything and it's all data anyway so interfacing one format to another doesn't make a real functional difference when done right, BUT, that's not really the question being asked, or the design of forge, there's other projects to cover that, things like FCL, UMC, and.... uh, actually, i probably can't say that last one im thinking of for a lot of reasons so, if you know, you know.
TL;DR, probably better for everyone to let a slightly older version stew, rather than chasing two moving targets.
