Immersive Railroading Mod 1.16.4 bugged?

I want to play with the Immersive Railroading Mod on version 1.16.4, but the Custom Curves bug around. You can actually make a custom curve up to 1000 blocks long, but for me it only works up to 200 blocks. I've also tried a lot of different Forge versions and emptied my .minecraft folder, etc. But nothing works. And the mod is only available once for the 1.16.4 so I can't try an older version there either.

Is the mod also designed for 1.16.4?

Otherwise it wouldn't work at all

Was that your help you stupid idiot