Here is an example of firewall rules that can be used for a minecraft server, to easier mitigate larger attacks...
In this firewall I used a special approach which is to block only illegitimate connections. This firewall MUST therefore be used with a "network" firewall that will block requests before they reach your server. Below is an example of a firewall "network" in OVHCloud.
This will ease bigger attacks from reaching their potential, so that they don't fully reach your server. This firewall template will go perfectly with it, aswell as with Aegis our advanced AntiBot and AntiCrash solution for your Minecraft server. Together these three are an unbeatable team and with Aegis extensive features, exceptional performance and first class support you are sure to have your server stay up and running without any issues.
Download the script, modify it, to adapt it to your own ports and run it.
Download and run the reset file in the repo.