I already searched all over the internet to fix this but cannot solve it still.

this is the error:
luckperms - Failed to validate connection me.lucko.luckperms.lib.mysql.jdbc.JDBC4Connection@5da79bc4 (No operations allowed after connection closed.)

I hope someone can help me
The credentials are correct, I changed the wait_timeout to 1800 already so I'm clueless now.

What are you hosting and controlling your server with (e.g. multicraft/vps etc)

I host it on a Contabo VPS and I use pterodactyl as panel. Also I use MariaDB for Mysql driver

Delete the luckperms folder. Let it regenerate the fully kill the bungee. Edit the config making sure the ports are open or if it's localhost then keep it as that. And the start the server once you have fully edited the config. I had trouble with single character database names/users and not fully making sure the server is off.

Only delete it luckperms on my Bungee server or all the other spigot servers as well?

Only bungee.

Try this: https://github.com/lucko/LuckPerms/wiki/Storage-system-errors

@BrainStone Did that already sorry...

@ICEconchy The bungeecord error has been resolved now my spigot server has this error:
(Connection.setNetworkTimeout cannot be called on a closed connection)

It is just weird that only luckperms has issues with the MySQL/MariaDB and the other plugins are working just fine....

Brainstone was correct - please read the details on this page. This isn't a LP issue.

https://github.com/lucko/LuckPerms/wiki/Storage-system-errors#mysql-no-operations-allowed-after-connection-closed-error

Alright so could you tell me why no other plugin on that server has problems with MariaDB and luckperms is the only one with this error?

Probably because the other plugins you have don't use a connection pool like LuckPerms does.

I looked at this link: https://github.com/lucko/LuckPerms/wiki/Storage-system-errors#mysql-no-operations-allowed-after-connection-closed-error

My error isnt stated there, I got this error in my console: luckperms - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@6eb81946 (Connection.setNetworkTimeout cannot be called on a closed connection)

Yes it is - you error is stated there.

me.lucko.luckperms.lib.hikari.pool.PoolBase - luckperms - Failed to validate connection me.lucko.luckperms.lib.mariadb.MariaDbConnection@xxxxxxx (xxx cannot be called on a closed connection)