"Apple Arm M1 Macs ship... tho don't expect all open-source apps to work"
Why would open-source "apps" not be ready for the new architecture. If we are provided with a C and C++ compiler, it is as simple as just building the source as usual. Since the API hasn't changed, there should be very few platform specific parts needing changing.
Especially since many of the x86 specific code has already been eliminated whilst "fun porting" to the Raspberry Pi. Open-source is really good here.
The main reason why iOS and Android are "hard" is because of the terrible toolchains and focus on vendor specific languages. And even then they aren't hard, people just lack interest for such short-lived platforms.