I have been unable to find any information on whether “find my network” works with all iPhone models including older ones (such as 8 or se2020) or not.
When I say “works” I mean both ways, i.e. to find your own OFFLINE phone and to relay information about other phones.
Surely this must rely on some specific, always on, hardware?
Can anybody point me to some relevant info?

Find My App: Everything to Know
Apple in iOS 13 and iPadOS merged the Find My Friends and the Find My iPhone apps into one app that's just called "Find My," because...

If the device is running ios 13 or later then it should work ....... the offline location works on bluetooth nothing special.