Sorry, there is one item I forgot to mention in the video, once in the APP Store, in the upper left hand corner, click on the "iPhone & iPad Apps" link or in the centre of the screen select the "See all iPhone & iPad Apps" link.
If that does not work, you may need to be signed into the APP Store with your AppleID.
Finally, if this is a new M1, my new M1 required several reboots when I was first setting up so please ensure all updates have been applied.
Let us know if you get this resolved or if I can be of further help.
Check out this short video where @Stu Rathbone shows us how you can run the ProntoForms app on your Mac (if you have a newer one). A great tip for sharing your forms on video calls or even speeding up your form building/testing!