A lot of developers are lured into building in a dependency on Google services, so yes you'll need microG or, as GrapheneOS prefers, the original Google code running on your device for those apps to function. Or patch the app, like Langis does for Signal (not necessary for it to function without Google in this case, but it removes its calling out to Google's apps and services for those who don't want that). If you're happy with that setup and don't need protect-from-the-government levels of security (street thugs aren't going to ransomware your device by abusing an unlocked bootloader or send exploit chains that work on anything but the hardened allocator), LineageOS is probably the better choice for you. GrapheneOS has some nice things like easily denying the network permission for an app (even if they could theoretically work around it with intents) and having a custom A-GNSS server, but you can do the same on LineageOS by using root and something like AFWall+ for the network and configuring Graphene's A-GNSS (SUPL) proxy in the system settings (don't forget to donate if you use it and are able)