Right, so this is really quite a mess. The post you linked to is precisely the issue I am having - thanks.
(The state of MariaDB in the context of CoreELEC)
Bit frustrating, as it happens, as when I moved all my service thingies to dockers, I went with linuxserver/mariadb (rather than say MySQL 8) - specifically because I don’t need a wizz bang up to date DB (for Kodi use only) - just something stable. So figured since this was the primary db from Linuxserver, it was likely to be the more stable option. Did not realise that MariaDB is, generally, in a bit of a bad state right now. (As I read it, it’s not really the update to Alpine as the underlying OS that’s the problem, it’s the update to the MariaDB version that came with it…).
I am in exactly the same state as this person:
https://forums.unraid.net/topic/40737-support-linuxserverio-mariadb/?do=findComment&comment=1030438
Thus I followed zoggy’s post and rolled back to the older version (deleting the mentioned files etc):
ghcr.io/linuxserver/mariadb:110.4.21mariabionic-ls31
…this seems the easier path, because I have a bunch of installs and I don’t want to needlessly go around adding no compression to them all in advancedsettings.
(But really wishing I’d just gone with MySQL 8 to start with!)
Edit - the above fixed worked and I can access the DB from both CE and Windows again, without issues.