Minecraft Server is not working and I've tried almost everything?

So me and a few friends wanted to create a Minecraft server, of course there are sometimes really cheap host providers, but I'm more the type who want to try everything myself first. Long story short I wanted to create a Minecraft 1.16.4 server, released the ports in my router, released everything that had to do with java in my firewall and reset my entire network once. Well it still doesn't work.

The screenshot of the Minecraft Error is from the client PC (friend) and all others from my host PC.

Can you rule out that you don't have a DSLite but your own real external IPv4 address?

Try to put the port back to 25565. And for this your friends have to connect via the IP that you have from your provider. So go to https://myip.is.

Oh I don't know how can I find out?

Okay I tried that with the normal port and with my provider ip but it still doesn't work.

That should be in DSL information or in the online monitor, somewhere then something is written about IPv4 over DSLite

Okay yes I have a DSLite connection

Then you can open as many ports as you want, it won't work ;-)

You can only be reached from outside with a real and own IPv4 address. IPv6 would work, but I have no experience with it.

You have to open a question that goes something like this: Make Minecraft servers accessible from outside with IPv6?

Okay then I now know why, thanks for the quick help

You could also test a service like NO-IP, maybe it would work. There are enough tutorials on YouTube.