No circle app icon shapes on Android 10

That option is handled by the stock launcher....
Install a different launcher from the play store, such as Nova launcher, which is what I use, and in its settings you can choose to use circle icons, or you can install an icon pack from the play store, and use them as your new icons also...
This is my icon setup...

 

FWIW I've got two devices here running Android 10, Huawei Mate 10 phone and a T95 Android box, and neither of which is showing circled icons by default. Although the Huawei phone has some icon themes with circled icons, that can be installed if I wanted from the Huawei "Theme Store" app.

This is apparently the stock icon set for a Google Pixel device with Android 10. Some apps are circle like icons, but not all, like Amazon. This is what comes from Google of course, and not some other manufacturer that might apply their own customizations.