Transaction check error:
file /usr/lib/systemd/system/mysqld.service from install of MariaDB-server-10.5.5-1.el7.centos.x86_64 conflicts with file from package nethserver-mysql-1.1.4-1.ns7.noarch
You installed the recent version from the mariadb site?
It seems that recent MariaDB versions want to use service mysql but NethServer already uses it for MariaDB 5 so there’s a conflict.