I'd like to help you connect your bank account to QuickBooks Self-Employed (QBSE). Can you share with me the bank account you're trying to connect to? This way, I'd be able to check if there are any related issues here on my end.
Additional information is appreciated. In the meantime, you'll want to import your bank transactions to your QBSE account. Let me guide you how.
Sign in to your bank's website and download your transaction as a CSV file.
Once done, sign in to your QBSE account.
Go the Gear icon.
Select the account you want to add the transactions into.
Locate and select the file, then click Open to start import.