"journalctl -b 0 --no-pager | paste" <= gives you the current boot (index 0) and sends to our pastebin site
"journalctl -b 1 --no-pager | paste" <= gives you the previous boot (index 1) and sends to pastebin
increment the index to get the right logs (that exhibit the issue) then share the pastebin URLs
General advice for CEC issues is .. turn everything off and unplug devices. Leave for a while. Connect everything and power back on.
It often makes no sense but has a surprising hit-rate for success 
The custom change in my image wasn't correct and the blacklisting prevents that change from being used anyway, so you should be able to swap to official images without problems. Go test and see.
NB: The "rtw88" driver supports a family of Realtek chips including PCI/SDIO/USB models and upstream driver code is modular, so rtw88_8822b is loaded when it needs to support USB devices and rtw88_8822bu has further code specific to that chip variant. It's how drivers should be written; with common code reused. The vendor drivers are "project" based; so each Realtek customer releasing a device gets their own code-fork and driver release with minor branding (and USB ID) changes and the world ends up trying to track 50+ iterations of the same driver.
Take the older image that boots (as it boots) and then update to the current LE12 nightly. Anything improved?
https://wiki.libreelec.tv/configuration/ir-remotes#configuration-advanced
Settings/System/Display - Official Kodi Wiki
Settings/Interface/Regional - Official Kodi Wiki
The answer to your next question is likely in the LE or Kodi wiki too. Please use them.
V3D is only for the Kodi GUI?
There's a hint in the name .. "3D" .. it's the mesa driver, nothing to do with video decoding.
Correct. Enable persistent logging in the LE settings add-on, and we need to see the system log (Kodi logs are irrelevant).
The Amlogic H264 decoder is more reliable than VP9 so I would favour that format. The refresh rate shouldn't matter, but I would recommend using adjust-refresh with 60/59.94/50/24/23.976 modes, see https://wiki.libreelec.tv/configuration/4k-hdr
Enable persistent logging (so logs are retained during non-Ethernet boots) and then share them. If you're lucky there's some error messages that provide clues to the problem.
Wireguard confs and systemd info are under /storage/.config and crontabs are under /storage/.cache
Assuming there is no media on the internal drive and you only need to move config data: IMHO it will be cleanest/easiest to back-up only the Kodi userdata folder on Ubuntu. Then make a clean LE install and "restore" the userdata folder to /storage/ubuntu. You can now stop the clean (empty) Kodi install and selectively move essential files back before restarting or rebooting to effect the changes: Library DB files, your sources.xml and passwords.xml and advancedsettings.xml files, and the contents of the addon_data folder. You can reinstall all add-ons from the respective LE or Kodi repos and they will reuse the existing (previous) config. I would let thumbs etc. download again and I would go through the GUI to set things as you like again: guisettings.xml normally contains some /paths/to/things for Ubuntu that are wrong with LE and those aren't automagically updated. Most of the time it takes 5 mins max to setup Kodi again. Take pics of the major screens on a phone if you need to "backup" things. If you are familiar with the major files Kodi uses and where things are located the entire process is a 10-minute job .. plus some time for thumbs to resync.
The current rpi-6.6.y kernel in LE12 images contains earlier iterations of the same changes. Once upstream merges the patches that are submitted to the mailling list the pi devs typically revert earlier changes and backport the now-merged ones to keep the kernels in sync. Then LE will pick the merged changes up in a future kernel bump.
NB: I wouldn't expect any noticeable performance increases. Rendering the 2D Kodi GUI is a simple task compared to the complex 3D game graphics used for the benchmarks.
If you reuse the SD card you will permanently overwrite the current/working install so I would recommend using a different SD card for AMLGX experiments. Then set the dtb name to use in uEnv.ini .. as per the wiki instructions.
If the device worked with the p212 dtb before (means the box is GXL/S905X) use the meson-gxl-s905x-p212.dtb file. If you use the p212 dtb file from the old LE image or gxbb/s905 dtb files from AMLGX image the box is not going to boot.
It sounds like the GUI is (correctly) showing IP info for the interface providing the default route to the internet. If you want to SSH into the device using some other interface you can look in settings > Network to see what IP has been configured or assigned.
systemctl stop kodi
rm -rf /storage/*That ^ should give you a system free of all the containerised piracy tools. Sorry if that's not directly answering the question.
Tried LE12 nightly 'box' image using ALL p212 dtb files (All s905x files) but no boot.
Also tested LE12 nightly 'Le Potato' image using Le Potato dtb and p212 dtb, both working the same!
This was already explained (twice). Thread closed to prevent need for a third round.
LE settings > System > Create System and Kodi Backup
.. and same for Restore.
This only captures /storage/.config|cache|kodi .. but for most users that's everything you need.
You can dump the existing database and then import the dump to the new database before changing advancedsettings.xml to use the new DB location. There are lots of howto guides for dump/import on the internet. Most of them aren't discussing Kodi database migration but it's nothing Kodi specific.
