We're talking about chat.. you shouldn't be logging the contents, at most a bit of metadata to prevent abuse (eg. a connection log to identify and block spammers).
If you don't store that metadata longer than needed (a couple of weeks? storing it for years would be hard to defend) you have legitimate reasons to keep it, and don't need to worry about deletion requests
That's why I mentioned I'm ok with projects reacting strongly and removing themselves. Removing my info (and many other GDPR points) is in my interest. If they can't do this, I'm glad I won't be their immortal user.
I was going to say the same thing. If you're an individual running an OSS service, or a small business, requests for information or deleting information really are going to be really rare.