When trying to install MariaDB 10.5, 10.4 or even 10.3 from your repos for CentOS 8, and on the side installing postfix with SQL support, which installs mysql-common, you get conflicting files between the two packages and postfix cannot be installed (or MariaDB cannot be installed if you installed postfix first, no matter what)
This is not resolvable by any exclusions as these are dependencies.
If you install mariab 10.3.27 from the CentOS repo aside with postfix this error does not occur.
So at the moment it is not possible to use 10.4 or 10.5 together with postfix on CentOS 8.
It would be nice if this could be fixed asap.