You want, I think, too many things: zoom lens, tele, decent maximum aperture, not-professional looking.
If I were you, I would eliminate the zoom-tele requirement, and go with something like this:
https://www.cameraquest.com/canql17.htm
Large aperture. Focus once with accuracy, remember where the focus is, concentrate on the moment. Minimalist enough not to be considered a real "menace" to copyright, yet providing a good lens and a good pocketability. I wouldn't go past ISO 400 and accept some degree of "movement blur" which can be graceful in a theatre picture. If you have a backseat, you take pictures of the entire venue, the atmosphera including the public, the special effects which involve the entire stage.
Everybody present will take their smartphone out to take pictures, so nobody should be worried for an ancient "unprofessional" film camera with no flash and fixed lens.
You will have to set exposure by "exposure tables" probably.
If there is a metal detector at the entrance, have it in your hands. If they object at letting this camera in (that would appear strange to me) have an alternative such as somebody accompanying you at the venue.