Here are the following scenarios why you're unable connect your bank account:
What you can do is contact your bank to check if for any maintenance update or request to establish a connection with QuickBooks.
If everything is good from your bank's side, you can follow these steps to search for the correct bank using the URL:
I'm adding this article for reference: What to do if you get a bank error or can't download transactions in QuickBooks Online.
You can also add the name of your bank and other details in the comments below. This way, I check our records for any investigations. Thank you in advance.
Thank you for the reply. These bank accounts were linked to QB before and ran multiple transactions, but since over a week they won't Update when I try to Connect and enter my Security Code (as before) and an error message shows up each time I try to connect: Something isn't working (see attached)
It helps to know that this issue might be caused by the bank and not by QB.
I thought eventually QB is doing maintenance as I can still log into my bank profile online without any issues and do transactions like before.
Hence I would have assumed that there is some kind of error on QB's side. But let me check with my bank consultant and see if he can assist me in fixing this.