Hello, i'm still new to multiplayer and i need help playing with a friend

I want to play this game with my friend together (me on linux (flatpak) and him on windows), but whatever i do i just can't get it to work.

I've gotten the ip for me and from him and everytime we join the other thru the ip option each of us just waits forever. I've tried to make it public on casual or standart too and that still didnt fix it since we couldnt find the other's lobby.

For both of us when we join the other it's always stuck on this screen:



I'm out of options and i would appreciate it if anyone has any solutions to this, Thank you!

A static IP address is required.

I'm Pretty sure you need to port forward https://www.jameds.org/portforward.html/

alright i did it and https://www.jameds.org/SRB2/ tells me "Port 5029 is reachable", but when my friend joins (i have my mods unloaded) he gets to the downloading game content screen (something in kilobits) he gets to 6.5kib/s and it drops to 0 then it loads but all he sees is black. in the chat i get the error "Sonic left the game. (Connection timeout). I checked versions from my game and his and its the same one.
I'm confused