Hey Martin,
I had tested your Qt6 and I think it is going great. I just had a little confusion between the releases 6.2.4, 6.3.2, 6.4.3 because I would expect for you to only focus on the lastest version and try to improve that, but you are working on those three versions at the same time 
Well the initial logic with 6.2.4 was that it was a Long Term Support version - except I didn't realise that after 12 months, the newer versions were commercial only for 12 months. Also, the 'delta' in the code was relatively short to 5.15. I wouldn't say I'm really working on 6.2.4 any more (other than recently dynamically linking the av1 video codec)
Stepping up to 6.3.x was supposed to be easy - except there are a few things not working.
6.4.x is the current main focus (until next week when 6.5.0 is released).
So whilst there have been 3 versions released, my hope is to get 6.4.x working the 'best' ASAP so that there will only be one version in development.
Hope this helps.