You'd have to post some links or information about specific issues for anyone to really know. NTLite is constantly updated, with at least a few updates every month and tries to stay current with every single new Windows edition and even insider previews.
In my experience browsing the forums and doing my own tweaking on 21H2, the majority of problems I've seen so far are Microsoft bugs or intentional decisions that they have to fix.
Windows 10 was fairly unstable for the first many editions, and you are really better off using a supported version like 21H2 now, because there has been too many bug fixes over the years. Any presumed performance increase you think you are getting by using an older version can either be achieved in 21H2 too and/or the bug fixes in later versions make up for it.
Until someone, somewhere, can show some proof that older W10 versions benchmark better under identical conditions, then it's all just hearsay. As a long time gamer I've honestly never experienced a situation where using older graphics drivers or older versions of OS's were better than newer ones.
Now with that being said, let me clarify that last statement, when I mean older versions, I'm talking about service packs within that same OS. So like I sincerely doubt W10 1809 beats 1903, nor does 1903 beat 21H2, etcetera. BUT, if we're talking about entire operating systems, like comparing benchmarks on XP vs Vista, or Vista vs 7 and so forth, then yes you will see differences because there are massive fundamental changes between those complete OSs.
I'm open to being proven wrong, but I need to see some benchmarks. And even then, if it can be proven that an older W10 version performs substantially better, it's just as likely that with minor troubleshooting you can modify some simple registry keys in a later version and get the exact same level of performance.