Hello Aylx and welcome to Apple Support Communities.
I see you have a question about the location reported by the Find My or Find My iPhone app (depending on if you're running iOS 13 or a previous version).
If Find My iPhone is offline or not working - Apple Support
If you've enabled the option to Send Last Location, then when the device is offline (including when it's locked) it will show the location of the last time the device connected to Wi-Fi or a cellular data network. You'll be able to see that location for up to 24 hours with this feature enabled.
Cheers.