There’s just no way. With PPC to Intel, there was Rosetta which kept compatibility for PPC on all Intel Macs from 10.4.4 (first Intel version) all the way until 10.7. Then, the 64-bit transition was a loooong time in the making but they first warned developers in December 2017 by requiring 64-bit in the Mac App Store, and external apps were still supported with a warning until 10.15 (released October 2019).
Switching to ARM would most certainly be completely incompatible. Unless they manage to pull off another feat like Rosetta (which would likely be MUCH harder in this case), it seems extremely unlikely that they would switch to ARM and break compatibility with all apps considering that they have yet to warn developers.
I think there’s a good chance, actually more likely than not that they will eventually switch to ARM for many reasons (efficiency, unified architecture across all Apple products, etc.) and some non-Apple portable PCs already use ARM. However I think that’s a long ways away, unless they run iPadOS. macOS isn’t ready for ARM.