From reading the Magic Earth FAQ, I believe the user data actually isn’t used for traffic at all (at least the manually reported events certainly aren’t).
Edit: never mind I missed a later part in the FAQ:
Do you share data with third parties?
We send position data to our traffic provider to generate real-time traffic information. The data is anonymized on the phone, using a changing key (so it’s not linked to you), and it is deleted after 5 minutes.
i use miracast where I can (my TV and Samsung phone support it natively), as it pretty much just works and is a decent protocol. Sadly every phone manufacturer that isn’t Samsung seems to have abandoned it right now, but it is still widely supported in TVs. On Linux, there is the app gnome-network-displays (yes it also works on KDE) to cast your screen over miracast.
Miracast is an actual local streaming protocol (closely related to WiFi Direct). For content streaming the only FOSS standard I am aware of is FCast, but sofar it only is implemented in the GrayJay Android app.
Edit: There is also Deskreen for casting a PC screen.
For casting mobile to PC there is also scrcpy.
This isn’t really casting, but I often find that an HDMI cable (often paired with a USB-C to HDMI dongle) is the simplest and most reliable way to display a phone screen on another monitor (as long as the phone supports DP altmode).