Hello there, @Bob M.
It could be Bank of America is performing system maintenance, or there are notifications that need your attention. That's why you're unable to log in through QuickBooks Desktop 2020.
You can sign in to your bank's website first to review its log files. This way, you'll be able to check for connection failure messages and address them with your bank.
Once done, go back to your QuickBooks account and let's download your transactions.
After you've successfully downloaded your transactions from Bank of America, you can add them to your account. Kindly refer to this article for the steps: Bank Feed transactions in QuickBooks Desktop. It also contains information how to match the transactions to the ones in QuickBooks.
In case you're encountering errors while logging in to your bank, you can refer to this article for the detailed steps on how to fix it: Fix OL and OLSU Bank Feeds errors in QuickBooks Desktop. It also contains an additional explanation about what causes the error.
Please let me know if you have other concerns. I'm just around to help.