how do i change an app that only shows in portrait mode to landscape on my ipad 7

Not all of the 3rd party apps can support landscape mode.

If it happens using that app only, contact their support team and ask them:--> How to contact an app developer - Apple Support

Regards

Giulio

Also bear in mind that if you download an iPhone app onto your iPad, they will not rotate to portrait mode.

It’s going to be fun to see what owners of new M1-equipped Macs make of this limitation...

I missed the event and have not read a thing about the new Macs. I am way behind on all of that.