Support intro
Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 20.0.5): 21.0.4
Operating system and version (eg, Ubuntu 20.04): unraid 6.9.2
Apache or nginx version (eg, Apache 2.4.25): latest nginx docker
PHP version (eg, 7.4): latest php docker
The issue you are facing:
all of my theming settings are no longer applied.
it was fine until mariadb automaticly updated
I tried to revert to the previous version of mariadb, no fix
I tried to restore a backup of nextcloud, no fix