Now i dont want to defend reddit here, but afaik most comments are not subject to GDPR as long as you dont know they contain personal data and they have been detached from other personal data fields (like username).
So by removing personal data fields, they most likely become "anonymized".
Of course thats not the end of it, you have to consider the available technology to de-anonymize this data for it to be legally called anonymized.

But i dont think there has been any case where this was challenged before.. and i bet most supervisory authorities would discard such complaints as being "too hard to follow through". (i got that reply from the Netherlands authority for checking newsletter opt-in from a website)
And i certainly dont think reddit or any operator will be forced to delete comments because they could be deanonymized depending on the content the user wrote, when most comments probably cannot be deanonymized.
Having to check everything for potentially identifiable data in that regard would be ridiculous.

Nope, your username and email are required and linked to your data, so it's entirely personal information. True anonymization is impossible with open text fields, as it's always possible that people reference other users within their posts, etc.

Of course, what the DPAs do with it, is another matter. Doesn't hurt to try.

Nope, your username and email are required

I have never used an email address with reddit. It’s not required.

You have to give one, while signing up (just checked); unless you go through apple or google ID services. Either way, they still log your IP and other meta data not to mention your username does exist.

no, you do not have to. You can just skip when it asks you for the email.