Last I checked, your more recent Lua was working fine for me under the uf2loader and 1.4 (official) BIOS. I was using JackCarterSmith’s BIOS for a little while in the past, but had an issue with it (I forget exactly what, but a few firmwares were being weird) so I rolled back to 1.4 for better compaitbility on the things I use.
I thought 1.2 was only needed for older firmware that hadn’t been updated in quite a while and was using the original hacks to work with the (kinda flaky) 1.2 BIOS from Clockwork. I don’t think there’s been a more recent lisp build, so that one might require it. Maybe some of the older MicroPython builds do too, and probably a few other things that have gone dormant.
The BIOS thing is kind of a mess at the moment, because there’s no single version that will work with every firmware, and I’m not sure that there ever will be. If folks need to stay on older firmware, then they’ll probably be stuck with the older BIOS, and its limitations. But so far it also doesn’t seem like there’s a clear way forward with a single new BIOS being adopted by everything. I’m hoping it eventually gets to that point. JackCarterSmith’s seemed like the best bet, but there are some other folks working on BIOS variants too, and I wouldn’t put much faith in the offiical Clockwork one ever being updated unless it’s just replaced by something else that becomes popular in the community, as was done with the initial loader effort (which unfortunately meant that ever new PicoCalc owner was confronted with the .bin loader which would never be updated or supported by firmware in the future!)