I can confirm that video calls work in Signal on Android flavors that don't use Google Play Services, including both GrapheneOS and LineageOS.
(Perhaps WhatsApp might work as well, since, IME, it can be sideloaded and will work without a functional Google Play Services.)
I'm confident Whatsapp will work, but I have not tried. Push notifications will not work without Google Play Services.
Discord works perfectly with microG, and has a 3/4 rating without it since notifications will only work if you have microG.
[1] https://plexus.techlore.tech/applications/whats-app
Push notifications are bad and it drains significantly more battery.