In the 12.6.0 beta code, Top Level Domains which are not country-specific are still not supported. For example, mine is a Donuts TLD, .systems. When I try to create a new user using my corporate email address, I get the following error:

WHD Is by no means the only culprit, but if you could bake in support for the whole range of TLDs, it would make the product usable for all comers. Here is an example list of those currently available:
List of Internet top-level domains - Wikipedia
Tagging milan.hulik for visibility.