They were doing a maintenance update today.   It is back online.  See this post for details to sign up for updates when they are doing this type of service:  https://www.artesanibookkeeping.com/quickbooks-maintenance-updates/

Resolution for 'bank connectivity issue: 'i am still having bank connectivity issues. even if i log in through a browser.' available: Yes.

The bank connectivity issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the bank connectivity issue yourself by looking for a resolution described in the article. If it is a complex bank connectivity issue or you are unable to solve the issue, you may contact us by clicking here or by using other bank connectivity support options.

For more information about resolving issues related to bank connectivity in Quickbooks/QBO or to get support for the issue 'i am still having bank connectivity issues. even if i log in through a browser.', click the link below: