Hey there, bgrebil.
Thanks for reaching out for support here in the Community. I want to make sure you're able to disconnect bank accounts in QuickBooks Online.
I appreciate the screenshot you attached with your question. You're looking in the right place for the "Disconnect this account on save" check box. As an initial troubleshooting step, I recommend clearing the cache within your browser. Sometimes the cache can become bogged down with older data, potentially affecting views and performance in QBO.
This article will walk you through the steps to refresh the browser: https://quickbooks.intuit.com/community/Getting-Started/How-do-I-clear-my-browser-cache-and-temporar.... You'll just need to select the particular browser you're using.
Feel free to let me know how things look after trying this, and we'll go from there. Take care.