It doesn't have a speedometer function, but I selfhost Owntracks for personal location tracking with my Android smartphone.

It has a back end that an android app sends location too, and a front end that displays those location points over a map. It can display lines between consecutive points, show a heatmap of the location points, filter location history within windows of time,, and more.

FitoTrack is a nice open source fitness tracker which shows the path on OpenStreetMap background. It logs position and speed data.

You can create a custom workout which shows you the current speed instead of average.

https://f-droid.org/packages/de.tadris.fitness/

What do you actually need it for?

I've been using traccar (https://github.com/traccar/traccar).
It's mostly for fleet management, but I've been using it as a replacement for Google maps timeline.
Its android apps ara basic but haven't had any problems with them.

Or if you find a service which doesn't provide a client you can use this app https://github.com/mendhak/gpslogger
It allows you to send the gps data to different services with their specific formats at the same time. I was using it to send the data to traccar while also saving it in a local file.