My samsung phone was stolen and I used the samsung find my mobile but it's been showing not connected to a network.. if the person flashed the phone would samsung find my mobile still work
You must be logged in to use find my phone. If its been factory reset there will be frp lock that will require your password to set up the phone again.
So if they managed to factory reset the device then find my phone will not work because your no longer logged in, but they shouldn't be able to use it.
If you catch your phone is missing very early on your able to use find my phone to lock the phone. This blocks settings changes and the phone can't be turned off.
they just need to wait for the device to turn off and flash the software altogether, at that point the samsung account is not liked to the device and you will not be able to locate it.
However from find my mobile you can see your phones IMEI, write that down and go to your local authorities to denounce the fact that your device was stolen, after doing that and getting the "denounce document" call samsung green number and tell them what happened or ask a mod here in the community, with the denounce you will be able to give samsung the imei of the stolen device and they will lock it completely and make it unusable for the one who stole it.
Unfortunately this is the only thing you can do