I have comaps from the fdroid store both on my last phone on stock android and my current fairpbone6 with CalyxOS.
It worked/works with android auto in both cases. You have to enable the setting to allow unknown app sources or something on older android like 12 IIRC.
New phone needed nothing to recognize fdroid apps. It even works only installing google and google TTS stubs and not the actual app, then using a 3rd party TTS like marmalade/supertonic