I like to play Minecraft and would like to know how to create a Minecraft Java Server with Raspberry Pi 4. Do I have to pay attention to any things that are important? Is there a way like e.g. Ngkrok to release the ip?
It is possible to host a Minecraft server on a Pi, but to explain that would go beyond the scope of the answer, you can google your own and would have to get many answers. You can handle port forwarding with ngrok as you have already written.
It is possible, I once did it with this video:
But I have to say let it be better for a Raspberry is too weak.
You only need java (sudo apt install default-jdk -y), and the respective .jar file, i.e. Server.jar from mojang for vanilla, there are separate ones for spigiot or paper, you can simply download the .jar file with curl, then you have to either release the port in the router or use ngrok if you want to play with friends, but the address changes every time, as an ngrok alternative I can recommend localtunnel, because you get a subdomain that always stays the same
No, I've tried it, it works great with paper, if you overclock the raspberrypi you can even run the server with mods
