Implementing email-less registration would be really hard on Discourse – see [Paid] Plugin- Allow no email address necessary on registration - marketplace - Discourse Meta (and several other similar requests in Discourse’s support forum.
I assume that the concern for not sharing an email address is privacy? If this is the case, what about creating a single-purpose free email address on a privacy savvy service like Tutanota or ProtonMail? (more alternatives exist, and I’m not a privacy expert)