So, let's talk instance size vs instance culture!
If you're not on one of the >50k instances: How do you deal with new users?
If you're on an instance with one or two major topics: how do you deal with new users who chose your instance randomly and aren't all that much into your topics?
Mastodon doesn't really have a way to introduce new users to the instance, and to help them integrate with their new instance's culture, rules, and maybe topics (if applicable). A welcome message could help …