Very early in the first Bitcoin boom cycle I had a friend who was into it, so I opened a Coinbase account because I thought it'd be funny to pay him the $15 I owed him for lunch or whatever in Bitcoin. I bought the $15 on a credit card, sent it to his wallet, we had our laughs about it, and I moved on. Years later, after it became clear that the only purpose of cryptocurrencies is scams & crime, I went to close my Coinbase account just for some basic digital hygiene. Except I found out that now, they only let you log in if you have an external bank account associated with your Coinbase account. And you can't delete your account without logging in. And there's no way in hell I'm associating my real bank account with a scam & crime agency. So I'm stuck with a Coinbase account I can't close or even log in to. Lol.

If you joined when Coinbase was still giving 0.1BTC signup bonuses, it might be worth trying to retrieve the account

There's a law for that. If Coinbase did not require an external bank account to create the coinbase account, by law, they cannot require one to close the account. At least, that is what I have been led to believe. You could sue.