When using an app in Landscape mode, you can open a second app while the other one is in the foreground. Just swipe inwards from the edge of the notch area to bring up apps or functions, click an app icon, then you can operate the app above the other one, in a floating window.
Multitask with the floating mini-app.

Go to [Settings] > [Smart & Convenient] > [Full Screen Multitasking] and toggle the slider to green.

• When the phone is set to block notifications and you receive new messages from quick apps, notifications won't pop up, while a red spot will display on the app icons.

• When the phone doesn't block notifications and you receive new messages from quick apps, notifications will be displayed with a banner on the top screen. Tap Reply in Floating to start full-screen multitasking.

Note: The Full-Screen Multitasking supports WhatsApp, Messenger, Line, and WeChat, but may differ between countries or ColorOS versions.

Add and rearrange quick apps. 

Tap [Quick Apps], then drag . Next, to move the app up or down. You can add up to 3 apps.

Rearrange quick functions. 

Tap [Quick Functions], then drag next to the function up or down.

Note: The quick app needs to support the floating window feature. If some of its functions aren't working properly, use the app in full-screen mode.

 

* Pictures, settings, and paths might differ from those of your phone, but these won't affect the description in this article.