FOSS Location Sharing App?

It's a more robust solution than you're looking for, but you can accomplish this using Home Assistant. Using the mobile phone integrations, you can share your location.

phonetrack nextcloud app for backend/website in combination with OsmAnd on your phone works great.

That isn't the main goal of dawarich but family location sharing is a recently added feature

A privacy preserving location sharing system that shows you a map can only work with offline maps. If the map data isnt already on your device, then that means the server delivering the map data knows where you are.

I dont know of an offline maps based live location app. There are plenty of non google apps that do this in a non private way as a primary or secondary function. Matrix/Element can do it and there are apps on fdroid (ToLoShare for example), that do it. But all of those have to somehow depend on a server that delivers the map "tiles" (chunks of map data near you) to show you a map. So they are all technically capable of tracking you.

The only really private way to do this is to share the coordinates through a secure channel in an automated way and then whenever you need it you open those coordinates in you offline maps app (CoMaps for example)

Zood location

Deltachat can do this

Reitti