Hey Members 👋! Hope you all are good 👍 😊!
So for tablet user as they want to get full advantage to big display over small display of smartphones but many apps have fixed rotations so they open in portrait mode and feels very uncomfortable with tablet so do the following.
Good Lock > Multistar
And to enable multi window for every app even on One UI Core
If One UI 4 or One UI Core 4 or higher,
Then go to settings > labs > multi window for all apps
If Ond UI 3/3.1/3.1.1 or One UI Core 3/3.1
Then go to developer options:
And turn on "Force Activities to be resizable"
Its experimental so it may work or may be not and some apps may not work properly
If you do have multistar:
Turn on "enable multi window for apps"
Hope You found this helpful and informative 👍 😀 🙂
A small proof 
