I'm afraid a chip cat flap is the way to go. It also is meant to withstand more force than a magnet cat flap.
My neighbours cat (Sammy Too) used to come in with his magnet. Then when he lost his magnet he regularly forced his way in, until he broke the mechanism. He tried a couple of times with the new chip cat flap and then gave up.
Chip flap installed; cat freaked out by the new clear door instead of the fogged up yellow Staywell door it's replaced. She's made it out now to see if she needs encouragement to come back in.
I'm afraid a chip cat flap is the way to go. It also is meant to withstand more force than a magnet cat flap.
My neighbours cat (Sammy Too) used to come in with his magnet. Then when he lost his magnet he regularly forced his way in, until he broke the mechanism. He tried a couple of times with the new chip cat flap and then gave up.