This is probably quite difficult to answer and also most like quite heterogeneous:
Many Raspberry Pi OS / Rasbian but again some Buster, some Bullseye
Probably some Armbian which is either Debian or Ubuntu based
Maybe some Ubuntus
From my understanding there are reports that some CAN stuff worked on 32bit kernel but not on 64bit, whereas I would believe that most of the recent installations run 64bit. IIRC the Raspberry Pi OS went 64bit beginning of 2022