Welcome to the Community. Yes, you can connect as many banks and credit cards with QuickBooks Online. Here's how to do this:
Go to the Banking tab, then click Add account.
Search for your bank in the search field.
Click Continue.
Enter the username and password you use for your online banking. Then, follow onscreen instructions if your bank requires additional security steps.
Select the accounts you want to connect (savings, current, or credit card) to QuickBooks, then select the account type from the drop-down.
Select the date range for the download, then select Connect.
In QuickBooks, you have the option to disconnect or delete a connected bank account. A disconnected account will still stay active, however, the system stops downloading new transactions. While a deleted account is permanent. However, if you have transactions associated with that account, it will stay in the checking account and will still show in the reports.
If you're unsure which is right for you, I'd recommend reaching out to your accountant.