Just tried the 10.0.1 release. My problems still exist (FF & rewind not working on MP4, TV remote not working). My 2 RPi3s (one for playing videos and one for TVHeadend) are still working fine. I've tried pretty much everything to get the RPi4 working - with & without Argon One case, different HDMI cables, different HDMI plugs on the TV, LibreElec, OSMC, XBian. With LibreElec I do note that with the RPi3 I get two messages about Pulse 8 connecting and only one with the RPi4 and I did find a comment on Kodi's site that there were problems with the MP4 format.
Unfortunately I don't have a second RPi4 to try so if anyone has any idea about testing it I'm interested.
I will keep trying nightlies to see if things improve, I can convert my movies to MKV (just have to dedicate a computer to doing it for a while), I can buy a FLIRC USB (as was recommended in response to an earlier post) but I guess that since the TV remote is IR that means organising things so the FLIRC USB is in line of sight to the remote and then there's this from FLIRC's website
Can I use my TV remote control with Flirc?
Yes, you can use your TV remote control with Flirc as long as your remote control has enough unused buttons and your TV does not respond to the ones you wish to pair with Flirc. We recommend using a universal remote control with Flirc for the best results.
ie pretty much no use (or maybe I'm misinterpreting) unless I spend more money with no guarantee of success.
Apart from throwing the RPi4 in the bin, or hitting it with a large hammer (highly satisfying - I had to do it once with a NAS) does anyone have a solution