I see the issue. Lemmy currently has a max post title length of 200 characters by default. This is enforced server side. I would argue that the server should be returning a more specific error message since the current one is very generic.

I don't want to hardcode a limit on the client since I think this limit can be changed server side.

The client does show a character counter once your title goes past 200 characters so at least you can tell how long the title is.