Huh. What manufacturer? When unlocked, stock Android has had incoming calls as a notification rather than whole screen for years.

When screen is locked it is probably still full screen.

Many crap reskins (Samsung, Xiaomi, Huawei) break the ability to hide call notifications. It's absolutely awful.

This is one of the problems of Android's model. By being so open to customization, any branch's weirdness gets mixed in with "Android", because there are too many variations and not enough linguistic ability to name them all clearly and consistently in conversation.

If I'm getting a call while using my Pixel, I just get a notification with quick-action button for accept, deny, and screen.

To be fair, the device is nominally a telephone with a few extra bells and whistles.

I didn't pay $1000 for a "telephone with a few extra bells and whistles"