Hello @lauramitchellcsx67
I had the same problem with my students, there has been some issues with the iOS and the updates. @domhnallohanlon has been really helpful with that.
What I did is tell my students to download Thunkable from the Test Flight. (Is the working version, they are just waiting to get approval from Apple)
This is the link: --> https://testflight.apple.com/join/7rBLpV07
Good luck 