Google Sign In hangs when signing in to YouTube

I have an issue that I can't seem to find information on anywhere.

I can't sign in to my Google account through YouTube on my iPhone. It works on my computers though and I have a completely healthy Google account according to its security check-up. I'll get to the enter email address stage in that app or browser and after tapping next, it just hangs on loading and never gets anywhere.

I've tried reinstalling the app, switching entire phones, restoring phones, etc.

Does anyone have any ideas?