To be fair, neither do we

For simple apps like that I usually check out F-droid see if any open source versions exist. Might not be as feature rich but there’s two GPS speedometer apps on there

Status Bar Speedometer (Display your current speed as notification) https://f-droid.org/packages/ch.rmy.android.statusbar_tacho/

Blue Square Speedometer (Simple speedometer & GPS viewer) https://f-droid.org/packages/net.nhiroki.bluesquarespeedometer/