Can I run old versions of (now incompatible) apps on MacBook Air?
Apple currently recommends that developers make Universal Binaries for BOTH CPU types. Are you sure that apps only support the M1 CPU and don't work on Intel? Can you give us some examples?
They may be advertising that they will work natively on M1, but I would still expect all Mac App Store apps to support Intel CPUs.
EDIT: The app is an iOS app, which previously would only run on iPads or iPhones. The new M1 Macs can also run these apps. It's unlikely that there was ever an Intel version of this app (as there are no Intel i-devices).