This is a small example of how to create/open a new, additional window during runtime of your Unreal Engine project and use any UMG UI Widget as its content to easily and conveniently populate the windows with whatever you want to put in there.
This sample is a C++ type project (the functions built in C++ can then be called from Blueprints, ofc) created using the "Early Access 2" version of Unreal Engine 5.
All C++ code should work fine with recent 4.2x versions of the engine, though.
The source code should be sufficiently commented to explain what's done, how and maybe even why.
Just open the project in UE5 EA2, or newer, and hit the "play" button.
No idea what else to write here.
If you have any questions, feel free to contact me on the above linked Twitter.