That’s not what this flag does – I don’t think there’s anything that actually skips renders.
Maybe you have a tick order problem?
You’ll want to detect the position, and set the cut flag, after physics, but before rendering.
The default is to tick before physics, so you’ll probably want to change your character tick time:
Of course, that means that controls will lag, instead, because tick phase is per-actor. Maybe moving the camera to another actor is the best option there.
Or, perhaps, your portal can have a trigger volume behind it, and in the “on volume overlap” function for the camera, you move the camera and set the cut flag?