@Nono Edit your /opt/fog/.fogsettings file and replace entries of ‘mysql-client’ with ‘mariadb-client’
I suspect they’ve updated the repo to solely exist for mariadb-client, but you had it before that package switch/change occurred so your fogsettings file is just expecting mysql-client always.
I might also recommend removing the existing mysql-client package just to ensure clean flow, though of course get a backup before any such actions.