MySQL Manager in CWP not working issues:
- list of databases is not shown
- can't create new database
- can't create new user

Most common issues are that you have added invalid config into mysql config files.
You can check this from the command line by using one of the following commands

mysql --version
mysql -e "show databases;"

For MariaDB which is default with CWP please note that you need to add config into file
/etc/my.cnf.d/server.cnf under [mysqld]