Contact management in Proton Mail is far too basic. As others have said, it seems an afterthought.

Contact groups currently require an email, since they seemingly are only meant to be used for mass mailings. In the real world, users group contacts for different purposes, and some contacts do not have email addresses. How about giving us the ability to create "groups" a different way. Perhaps applying a tag, or creating folders, or simply add contacts without emails to groups.

This is not a hard computer science problem. Almost every other email provider has figured it out.