I'd like to know which bank you're trying to connect to QuickBooks. This will help me verify and check for any open investigation.
In the meantime, Let's try to connect your account using a private browser to help us determine if this is a browser-related issue. To open access to QuickBooks using a private browser, you may use either of these shortcut keys.
To start off, you can use an incognito window to access QuickBooks. Then enter the updated bank website URL. If your bank will appear in the suggested banks below the search field, you can continue the process. Then, go back to your regular browser and clear the cache. If not, you can use an alternative browser or you can request support for your bank.
You can also read through these articles for the detailed steps:
Also, I've got these articles for reference:
Keep me posted if you have any other questions with connecting your bank to QuickBooks Online. I'll make sure to get back to you as soon as I can. Have a great week ahead.