Some apps may still rely on the mysql default collation so changing it may lead to problems.
But the problem is not only the (default) collation. It could be defined as we like at db creation.
Nextcloud for example needs some more mariadb default settings for using utf8mb4 that may affect other apps, new database creations or backups.
Here is a discussion about changing collation for Nextcloud with more details.
CentOS 8 provides mariadb 10 so maybe for NethServer 8 we can think about
- using better settings from the start to allow a wider range of possibilities
- or just run another mariadb instance with more modern settings for apps that need it