Hi, i had a need to do this for some of my apps.
I added the solution as part of a plugin called EnhancedUi. Which is mainly tools to build “Editor Like” UI/Ux at runtime.
In short you can use the UMG Splitter(from plugin too) and the Viewport Window…
Ive also given a more detailed answer here : Split viewport into areas of different contents
The guide : UE5 Separate Viewport From Widgets: EnhancedUI – Enhanced UI Plugin
The pluign on fab: https://www.fab.com/listings/b8777f94-8b76-4af9-a110-3c6329b31d06
Free Shipped/Packaged game to test: Unreal Musician on Steam