My experience is in big scientific experiments like particle accelerators, I guess other fields are different. Still, my experience is that:

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.