how to open 3 apps at a timeon ipad min 6 ios 15.4.1

Hello trido.

Thank you for using Apple Support Communities. To view three apps at once, you might be able to use Slide Over and Split View mode at the same time. First, have two apps open in Split View as shown here: Open two items in Split View on iPad - Apple Support

Follow the steps listed under "Open a second app in Split View". Once you have your two apps in Split View, swipe up from the bottom center of the screen to bring up your Dock. From here, try to long press a specific app and drag it over your apps that are in Split View. This should have the third app open as a floating window over your two other apps in Split View. Let us know what happens when following these specific steps. Cheers.