1) The control network is air gapped, any kind of direct Internet connection is very much forbidden.
2) Embedded real-time stuff usually runs on VxWorks or RTEMS, not Linux. If it is Linux, it is an specialized distro like NI Linux.
3) Anything designed in the last 15 years uses ARM. Older systems use PowerPC. Nobody has used Alpha, HPPA, SH4 or m68k in ages. So if you really want to run Debian on it, just go ahead and use Armbian.
It’s absolutely terrible for security but remote visibility into how your 100 ton haul truck is operating via some cloud API is what people like and keep buying.
No air gap, just hooked up to a cell phone network with maybe a VPN if you’re lucky. Either way, the kernel is handling packets directly from the Internet and keeping the kernel up to date is critical.
John Deere, Caterpillar, etc are leaning heavily into the “connected industrial equipment” world. GE engines on airplanes have updatable software and relay telemetry back to GE from flights.
The embedded world changed. You just might have missed it if your view is what shipped out before 2010.