I once had a fintech account with a company that is EU regulated. It was a long time ago and I used it for a couple transactions that resulted in a 0.27 Eur dust balance. I didn't use it after that and a couple years before Covid they decided they need more KYC to keep the account active and I just ignored them. To this day I still get emails about my remaining balance roughly every quarter. During this time (7 years…
They can close it, banks have no problem closing accounts with residual balances and they just keep the money if normal fees exceed the balance. Too much time is wasted discussing with various bots and call centre-based "customer support" these days. Normal procedure is/was to send a letter instructing them to close the account and to let them deal with it.
So there’s no impediment here to closing accounts after a few years of inactivity, whatever the balance (if it’s positive) it just has to be sent there.