Something doesn't add up here.
Your on-board Nuvoton w836x7hg is supported by linux kernel RC subsystem and should work with ir-keytable / rc_maps.cfg configuration, as described in the wiki.
However the uirt2 driver you mentioned is an external USB device and has nothing to do with the on-board nuvoton.
so long,
Hias
LibreELEC uses the modern in-kernel rc-core framework for infrared remote - read all about it here: Infrared Remotes [LibreELEC.wiki]
so long,
Hias
Just write the img.gz to a SD card (without pinn or a clone of your old installation), then config.txt and cmdline.txt are up-to-date and you don't have to worry about old kodi settings interfering.
so long,
Hias
If you want to test the nightlies better use a separate SD card for now and do a fresh install with the img.gz.
Updating from 9.2 isn't something we support ATM, you'd manually need to at least replace config.txt with current version, maybe also cmdline.txt if you changed something there, as lot of things have changed, and there's no easy way going back to 9.2 except restoring a full backup.
so long,
Hias
See here for more info: RE: LibreELEC (Leia) 9.2.5
With updated firmware my Pi400 managed to boot fine.
so long,
Hias
2.4.6-Leia is the latest official release and we are shipping that in our repo (the .1 at the end of "2.4.6.1" is internal LibreELEC revision number).
No idea what 2.4.6.4/5 should be - that doesn't match any tag/release in the repo Releases · peak3d/inputstream.adaptive · GitHub
We can (and will) update the addon when a new version has been officially released.
so long,
Hias
I ran into this issue as well 
rpi-eeprom-update fails on non-RPi-OS systems due to missing dpkg md5sum file · Issue #237 · raspberrypi/rpi-eeprom · GitHub
Fixed rpi-eeprom is included in linux (RPi): update to 5.9.0+ by HiassofT · Pull Request #4593 · LibreELEC/LibreELEC.tv · GitHub
so long,
Hias
Scroll down a bit on the wiki page to the "Making keytable configuration permanent via rc_maps.cfg" section Infrared Remotes [LibreELEC.wiki]
so long,
Hias
Please have a look at the wiki page Infrared Remotes [LibreELEC.wiki]
Delete the lircd.conf file and just use the xbox_one rc keymap, that should match your remote.
so long,
Hias
I really think this should be solved in libcec, or alternatively in kodi, by eg providing some quirks options to workaround the issues with your TV. TBH that issue doesn't really sound like it would be specific to LibreELEC, probably libcec/kodi on Windows would have the same problems - solving the problem at the core would benefit more users.
so long,
Hias
The firmware and kernel on LE9.2 is a bit too old, LE 9.2.5/9.2.6 will run with limited support (probably no wifi/BT) on the Pi400 if you replace http://start.elf/fixup.dat with the latest http://start4x.elf/fixup4x.dat files from here firmware/boot at master · raspberrypi/firmware · GitHub
LE10 will fully support the Pi 400.
so long,
Hias
You still haven't answered the main question: does that improve something?
We discussed that internally a while ago and decided against switching pulse 8 CEC to the kernel API and enabling CEC RC support for various reasons:
In passthrough mode core CEC will still be handled by libcec so the kernel driver only acts as a rather simple transport device. If pulse 8 decides to change something in their internal device communication protocol we can't simply update libcec but will have to wait for kernel patches to appear - which can be a real PITA, especially as we have to also care about older kernels during stable releases and testing bleeding edge kernels during development. It's best to avoid adding unneeded dependencies.
Upstream kodi and libcec are mainly tested and used with userspace pulse 8 integration. Again, there'd need to be really strong reasons (which I don't see ATM) to deviate from that.
So, to sum it up, the pulse 8 kernel driver is great if you don't want to use libcec, but as we / kodi already use that there's little point in doing a switch.
so long,
Hias
heitbaum now the big question is: does cec-ctl work better than cec-client?
We deliberately use libcec for the pulse 8 adapter (and not the kernel driver) as that's the software developed by pulse 8.
So if there are issues with the pulse 8 adapter or libcec it's up to pulse 8 to solve them.
so long,
Hias
will there be another Leia Release with Kodi 18.9 ?
yes
heitbaum here's a test build with the PR included, should save you some time building yourself
LibreELEC-Generic.x86_64-pr4627.img.gz
so long,
Hias
Linux kernel CEC support isn't currently enabled in Generic images. I've created a pull request to add that (and the SECO driver you refrerred to)
Can you give that a try?
so long,
Hias
Please create a separate thread for your Generic/NUC issues.
so long,
Hias
For 2ch/stereo keep passthrough disabled.
Passthrough is only needed if you connect a DTS/AC3 capable multichannel receiver via S/PDIF and want to be able to play back DTS/AC3 5.1.
so long,
Hias
