Earlier quoted context omitted.
I've never seen an app that required a FB or Google login. It was always possible to use email+password.
Pokemon Go's account own doesn't work. Even if you manage to create that account, it won't log you in. With Google account it works as expected. I tried to create two Pokemon Go accounts, gave up and created a Pokemon Go only Google account for child's playing. It has worked a few years.
This was the first month of Pokemon Go years ago. I haven't heard of it being an issue lately but I also haven't needed to create an account in a very long time.