Short update:
Kernel 5.10.1 update and a first version to fix seeking with H264 (and MPEG2/4 on RPi2/3) hardware decoding were merged into master yesterday and are now in nightly builds.
CEC on RPi2/3 should work again and H264 hardware decoding is now enabled by default on RPi4.
H264 seeking isn't perfect yet, sometimes it jumps to the beginning of the file (this is being investigated). You may also notice a bunch of ERROR lines in kodi log when seeking, these were (temporarily) added to make debugging seek issues easier - just ignore these if seeking works fine for you.
Video occasionally cutting out on RPi2/3 is still an issue, this is also being looked into.
so long,
Hias