Hello there, @MRusty.

We can enable the Track classes feature in QuickBooks Online (QBO) to view the Warn me when a transaction isn't assigned a class checkbox.

Here's how:

1. Go to the Gear icon.
2. Under Your Company, click Account and settings.
3. Click Advanced, then select the Edit pencil icon under Categories.
4. Turn on Track classes.
5. Untick the Warn me when a transaction isn't assigned a class.
   
6. Click Save, and then Done.

You can check these articles to know more about class tracking and how to assign transactions by class: 

• Set up and work with class and location tracking
• Track your transaction by class

Please let me know if you need further help turning off the pop-up alerts. Enjoy your day.