If you want to register participants by their email address, just make sure you aren’t using any other authentication profiles (e.g. participants must have a Zoom account or participants’ email addresses must be in the allowlist of specified domains) as these can mess with registration.
If you’re doing registration properly, you shouldn’t need any authentication profiles as the registration will be more precise than those authentication profiles can be.
This whole thing opened up a huge can of worms for us where we ended up discovering many more limitations to trying to have registered meetings on Zoom, but this is probably no longer the place for those issues.