Use case or problem
When typing the title of a note manually you cannot type specific characters, which is fine. When copy&pasting a title from somewhere else (e.g., a paper title) obsidian does not give you a hint that you just copied in forbidden characters. Instead, when pressing ENTER you get the error message and the title gets deleted. This is frustrating, especially if you edited the title after pasting and now you have to do the editing again.
I can think of two possible solutions:
Obsidian automatically replaces/removes forbidden characters when the user tries to paste them. Obsidian could also show a message that it removed the forbidden characters.
Obsidian shows an error message and blocks pasting title if the pasted content contains forbidden characters.
I think 1 is the better option, because if you cant paste the title you need to edit it somewhere else and that is painful too.