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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?

If the device is running ios 13 or later then it should work ....... the offline location works on bluetooth nothing special.
 
What makes you say that ?
I found an article on wired, but annoyingly I can’t find it anymore.

In any case, either it is always on or it isn’t, in which case is not entirely true that your phone can be located all the time.
It can be located as long as some connectivity (either cellular/WiFi or Bluetooth) is enabled.
 
What makes you say that ?
Here is the article:

Actually it says that Bluetooth signals are emitted even when offline, which I originally read as ‘even if Bluetooth is offine’.
I can see that it was my assumption.
 
I could see some people wanting to disable it so they don't accidentally send the position of a device they stole to its owner...
That was one of my guesses, although unless they can really limit proximity to other people then nearby phones will find it.

…or turning off the setting on a partners phone so they won’t get alerted of an air tag placed with them, for cases of suspected infidelity.

I’d legitimately appreciate hearing the perspective of what about this feature makes individuals want to turn it off. especially if it’s privacy, when your location is frequently tracked using IP, cell, and WiFi without your consent or explicit benift.
 
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