I Opened a nether Portal

What I expected to happen: I can see through the Portal

What happened: See Screenshot

BP Version: latest MC 1.12.2 Forge 14.23.5.2847

if any information is missing inform me and i add it

You've enabled the debug view, so that's what you're seeing.

And how do i disable that?

In the ingame settings (via Mods -> Better Portals -> Config) or the config file.