Welcome to the Community, @sdowell.

We can turn off those pop-up alerts by updating by going to your Account & Settings page. Let me guide you how.

1. On the Gear icon, click Accounts and Settings.
2. Click on Advanced and choose Categories.
3. Under Track classes, untick "Warn me when a transaction isn’t assigned a class."
4. Click on Save.

Please read this article for more information on classes: How Do I Set My Advanced Company Settings?

If you have other concerns, feel free to leave a comment below. I'll be glad to help you.