I experience the same issue, self hosted instance, with rising numbers. It started with sporadic registrations 1 or 2 a week. This week were 10 registrations, 5 even yesterday.
The pattern is a random string in the Pronoun setting and the already mentioned patterns in first and last names.
I do whois IP queries and over 90% are from 2 cloud providers in the US. So I started blocking networks instead of IPs. The risk to block regular users is very low when blocking cloud provider networks. Most are /24, some were /23 or /22 networks.
Often I get a bounce message for the registration email, because the email address is not available. There is also a pattern in these addresses. The common part is a subdomain, their domain part starts with a single letter subdomain like ...@a.example.com. I’ve seen letter a, b, c, e so far.
This could be a good attribute to block with Blocked email domains if it only allows regex patterns. A simple @[a-z]\.* could stop these attempts.