To explain it... whole process was utterly stupid, and works stupidly for no flippin reason. I downloaded the ojdk v17 msi installer from microsoft and installed that, then downloaded the ojdk v20 from java's own site, unpacked it to a different place THEN changed both Path and JAVA_HOME to point at the v20 folder.
After that it worked by starting the jar directly, as the exe loader does NOT work with this particular compiled jar.
Also, cmd correctly reports v20 being the active java version, but LT still loads v17. Probably insinuates a bunch of what I did was totally superfluous and unnecessary.
Do I have any explanation for why all these crossed wires doesn't explode majestically? Nope. It just works for some reason. Pretty well too in fact. No idea if it'll even work for anyone else though. Computers are an outright mystery at times...