I appreciate your time coming back here, tim39. 

QuickBooks Online will always default the date to the most recently entered transaction. For example, you record a Single time activity and manually set the date to 12/01/2020. Once you've saved and closed that transaction, you'll see that date will automatically be set the next time you go to create one.

While we're unable to set a default date in the settings, what you can do to make QuickBooks Online pre-fill a transaction's date as Today is to manually change it.

You can also follow the troubleshooting article provided by my colleague IamjuViel. 

I'm always around if you have any follow-up questions or other concerns with QuickBooks Online.