The challenge arises when an admin does not want to spam a link in a public chat (inviting raid attacks) or when you do not trust the source of the link (potential phishing). To join without a link, you must bypass the URL mechanism entirely.
Telegram is an encrypted fortress, but a careless link is a drawbridge left down. Lock it up. Join without the link. how+to+join+telegram+group+without+sharing+link+verified