Add the following line: deb http://apt.osmc.tv buster-devel main
Run the following commands to update: sudo apt-get update && sudo apt-get dist-upgrade && reboot
Your system should have have received the update.
Please see if the issue is resolved.
I also recommend you edit /etc/apt/sources.list again and remove the line that you added after updating. This will return you to the normal update channel.
Unfortunately, installing X11 has a tendency to break things on OSMC.
On your log I counted around 60 libx packages that probably needed to be deleted, along with x11* stuff. Just make sure you don’t delete these four, which are nothing to do with X11.:
osmc@osmc:~$ dpkg -l libx\*|grep ^ii
ii libxkbcommon0:armhf 0.8.2-1 armhf library interface to the XKB compiler - shared library
ii libxml2:armhf 2.9.4+dfsg1-7+deb10u2 armhf GNOME XML library
ii libxslt1.1:armhf 1.1.32-2.2~deb10u1 armhf XSLT 1.0 processing library - runtime library
ii libxtables12:armhf 1.8.2-4 armhf netfilter xtables library
My suggestion at this point would be to first try with the latest image on a second SD Card to see if you can get your display working than can rework that into your current system.
After about one month without being able to use the mediacenter and after dozens of trials and tests my solution to was to clean install previous version and disable upgrades.