Been following these discussions for many years, but first time to post.
I moved from OSMC about 1yr ago. It still runs on my backup system and it updated to Kodi 19 a while ago.
Some of the updates for my add-ons rely on Kodi 19, so I was keen to update LibreELEC also.
It's running fine for me so far on my RPi3.
So for anyone interested the steps I took starting with info from https://wiki.libreelec.tv/support/update
1. backup (maybe save backup to PC for safe keeping - takes a few mins)
2. Download update
Index of /
select latest rpi2
(.tar used for update, .img.gz for fresh install)
(I used LibreELEC-RPi2.arm-11.0-nightly-20211210-7f19d9f.tar)
3. Using WinSCP (or SSH) copy .tar to RPi2/3
/storage/.update
4. reboot - will load update
5. restore backup
6. Reconnect WiFi
7. reboot again
8. Check libreelec repos
Found that libreelec repos not showing all add-ons, only showing 1 or 2.
Went to add-ons, click left into Options window (left window), clicked update and found that repos were now showing.
(may have needed a couple of reboots, I can't remember the exact process to get it going)
9. If using Tvheadend
Reinstalled/updated Tvheadend 4.2 - TV now working using backup data (did not need to redo channels, auto record etc).
10. Check add-ons
Good luck.