Cash App is a mobile payment service owned by Square Inc., which is a financial technology company. Cash App itself is not a bank, but it allows users to send, receive, and store money.
However, when you add money to your Cash App account, the funds are held by a bank called Lincoln Savings Bank, which is a member of the Federal Deposit Insurance Corporation (FDIC). The funds are insured by the FDIC, which means that they are protected up to $250,000 per depositor, in case the bank fails. https://www.kivodaily.com/technology/get-the-up-to-date-cash-app-bank-name-for-direct-deposit-with-routing-number/