How do I find my Mac, even though it’s offline?

2 things are required to find the location of a device

1. internet connection
2. a it knowing it's location macs does not have gps build in so they rely on asking the internet router if it knows if it does not then the router asks the router it's connected to and so forth

there are not some special other means of locating devices

If your Mac is lost or stolen - Apple Support

You will need someone with remote viewing capability as an offline device is invisible to the network resources that are necessary to find it.