Currently LibreELEC-RPi4.arm-9.80-nightly-20210226-e12ff43.tar 2021-02-26
A couple months I am upgrading almost daily, the first upgrade was over LE 9.2.6.
There are still some issues, like with timeshift, but I never had an issue which should prevent TVheadend backend from starting.
You can perhaps also try to install Tvheadend 4.3 from ,zip ( Tvheadend nightly builds for LibreELEC ), I did not try yet and I am still running 4.2 which is part of LE 9.80 Nightly.
Anyone was able to start tvheadend with the nightly build?
Of course, it works fine. Try a fresh install from scratch then.
Try latest LE 9.80 Nightly build (Index of /).
In past, I have also encountered occasional i2c errors related to DVB-T2 tuner (which stopped working then), usually after switching channel, but now it's OK.
Yes this should be possible (TV won't get audio if you configure it to second HDMI port). The Receiver needs to be active so Kodi can detect it at (re)start. Did not test it on recent LE 9.80 Nightly but it was working like this couple months ago.
As a workaround I have installed a blank MSDOS formated SD card, with this arrangement the errors go away. Any advice would be welcomed, some more info…
This is not necessary. Just insert dtparam=sd_poll_once=on to /flash/config.txt file to stop filling logs by mmc0.
I don't use crontab but regarding to (re)boot, /storage/.config/autostart.sh works fine for scripts that you wish to run at startup.
Just a default setting should be OK.
Go to TVHeadend (http://libreelec:9981), Configuration - Channel /EPG and put your preferred channel numbers to Number column, click Save, then restart Kodi (systemctl restart kodi) or reboot LibreELEC. It will work.
You can use almost any Remote Control with kernel IR drivers using GPIO pin at RPi 4B, if you create your own custom keymap file (by editing one of most similar default templates). Even without Harmony. Just use a Remote Control from an old TV. There are many examples here, how to do it.
Perhaps look here, the difference for Argon ONE would be to use GPIO 23 instead of default GPIO 18.
RE: LibreELEC 9.2.6 Raspberry 4 and IrDA Dongle
If you have the Harmony, look here: Kodi, Harmony, and Raspberry PI 4 with IR sensor newb guide
Just use .gz file for upgrade to official LE 9.2.6.
For LE 9.80 Nightly test builds you can find the .tar files here: Index of /
Check the /flash/config.txt file and make sure it contains this line, which enables the analogue jack :
dtparam=audio=on
If there's not such line or if it's commented by # , edit the /flash/config.txt file ( Config.txt - LibreELEC.wiki ) to add it or uncomment and reboot the device.
Then you can set the analogue jack as output device (in LE 9.2.6 also together with HDMI audio) in Settings / System / Audio /Audio output device .
If everything is set properly and audio output through analogue jack still does not work, you may perhaps try another options: Onboard analogue audio options in config.txt (3.5mm jack) - Raspberry Pi Documentation
Or start with a fresh and clean installation of LE 9.2.6 to make sure there are no incompatible add-ons installed and it will work.
No problem, I'm glad I could help. 
FYI there's also a fresh how-to made by Skripo here: Kodi, Harmony, and Raspberry PI 4 with IR sensor newb guide
Regarding to rc-empty - I don't know, perhaps the -c cleared the default keymap. I have never used that parameter so I don't know details.
Or it depends on .toml file structure which is maybe missing some keywords, I really don't know.
I think the Default keymap is assigned by kernel driver when the IR device is detected.
Probably it does not matter if there's rc-empty when everything is working fine. And when it stops working, you know what to check / how to make it working again... 
Great, a good work!
Fixed in LE 9.80 Nightly build 20210128. Thanks for a quick solution!
Try to do what's described here: RE: LibreELEC 9.2.6 Raspberry 4 and IrDA Dongle
( a solution should be to use ir-keytable -a .... )
In LE 9.80 Nightly builds there're newer drivers so the mapping files have a bit different structure ( and .toml extension) but in general it's the same (also the older files without .toml extension are supported as well).
I believe this thread should be marked as Resolved as you are asking off-topic quiestions here which you should perhaps ask in your another - original thread... But hopefully you can finish what you need if you follow instructions already published here: RE: LibreELEC 9.2.6 Raspberry 4 and IrDA Dongle Do not disable anything, do not use -c parameter, just make the config files properly ( use some of example / default mapping files from the /usr/lib/udev/rc_keymaps folder as template, which is most similar to your remote control - the first line is important ), put them to override folders and use commands mentioned in the linked thread and that's all...
Maybe a small tip - search the default mapping files for a protocol that you are looking for, for example:
grep -rn '/usr/lib/udev/rc_keymaps/' -e 'rc6'
It will list the files that might be interesting for you.
Read carefully here: Infra-Red Remotes - LibreELEC.wiki
Use override directories to put updated files there as described in wiki. Do not try to modify the read only filesystem.
Use a working SSH client instead, I hope Putty could be usable: PuTTY SSH client for Mac OSX - download and tutorial
I would not try to modify the LE filesystem this way. If there're hidden folders, there's perhaps a reason why... And there's no issue to access them.
