I would really like to see the 5.1.0 version of the mod for 1.20.1, since the version in 5.1.0 fixed bug #192.

Agree with this. have had this issue for quite awhile now, and without the bug fix mentioned it becomes quite unbearable to explore caves when it occurs, without a consistent way to fix it. I am aware that it might take a lot of work on your side, but It would be much appreciated and not go unnoticed.

attached files show how the fake chunks aren't updated nearby the player, causing the lighting bug.

I will generally not be spending time backporting things.
If you want the latest features and bug fixes, use the latest version.

@Johni0702 I would appreciate if you could backport 5.1.0 to 1.20.1, as there is no point fixing an incompatability if you're not going to publish the fix for the correct version. See #192