Edit: Solution is in Nginx I disabled these: Cache Assets, Block Common Exploits, Websockets Support.

I can login using the local IP 192.168.1.2:9101, but when I route that with Nginx, It won't.

I have the GUI listen address as : 0.0.0.0:9101

I've been googling for hours but I can't find anything, In browser console it says

Failed to load resource: the server responded with a status of 403 ()

syncthing.my.domain.com/:1  Refused to execute script from 'https://syncthing.my.domain.com/meta.js' because its MIME type ('text/plain') is not executable, and strict MIME type checking is enabled.