Opening size is different from cutout size
Manufacturers publish several dimensions: exterior frame, hole required for installation, tunnel depth and the actual flap opening. Only the flap opening tells you the smallest space the cat must physically pass through.
Sure Petcare lists the larger Microchip Pet Door at 7.5 inches wide by 6 11/16 inches high. The standard Microchip Cat Door opening is smaller. Do not confuse the wall/door cutout with usable passage size.
Body width matters more than weight
A heavy but narrow cat can fit an opening that a lighter, broad-chested cat dislikes. Measure the individual cat rather than choosing from a weight chart alone.
A pet door should not require the cat to compress hard against the frame during normal use. Add practical clearance, especially if the cat moves quickly through the opening.
Installation changes the tunnel experience
Wall installations create a deeper tunnel than thin-door installations. The flap opening may stay the same while the passage becomes longer. Some cats tolerate that easily; others hesitate.
Before cutting a wall or door, mock up the opening with cardboard so you can observe whether the cat passes through comfortably.
Bottom line
For a large cat, buy based on clear opening size and real installation geometry. Smart access control is valuable only after the physical fit is solved.