its a bit 50/50 on where you’ll get the best answer, sometimes I ask in both places and add links to the two places.
Saying that I found a couple of things you can do.
Here are both the options, if you have a Camera Actor, you can change its aspect ratio so. Once you do that you can select it and either pin the PiP or split your view and change one of them to the Camera Actor - it shows the aspect ratio.
If you normally spawn a camera at runtime I’d make the camera a BP and have it destroy itself on begin play or in its construction script.