Hi,
I have a Pi 4 which was previously running a build of Libreelec with a workaround for H265 hardware decoding.
I’ve installed the December 2021 OSMC Pi 4 image on the device today, and run into various issues related to the OP (TV displaying ‘no signal’ following initial setup).
Initially I had the Pi connected to a monitor via DVI; whilst the display worked during and after setup, neither H265 or X264 playback appeared to use hardware decoding. I located a forum post which suggested that connecting to a standard TV via HDMI resolved the issue.
I reinstalled the December 2021 Pi 4 image, connected the Pi to the 1080p HDMI TV, and ran into the same issue as noted in the OP.
I tried using the August 2021 image, as noted in an update on the original post, but for me this didn’t resolve the issue - during the initial setup the display is fine, but after the system reboots, the OSMC logo is briefly displayed, then the TV shows ‘no signal’.
Any solutions gratefully received!