I own a 2018 11" and an M1 12.9" and there's plenty of times the 11" has failed to cope with something the 12.9" barely breaks a sweat over. I'm not sure what you do with yours, but it's provably untrue that there is not a single app that makes full use of the increased CPU power of these new iPads.
Cubasis / NanoStudio / AUM / AudioBus etc. Anything you can host multiple AUv3 instruments and FX in. The M1 handles many, many more AUs - depending on which ones, probably twice as many or more.
