notnn you can use signal without play services, you just have to change its battery setting to "unrestricted".
It's a bit more involved than that, but the sentiment remains.
There is no need to change Signal's battery profile, but you do need to ensure that the Play Services/Store apps aren't present within the same profile as Signal when it is first installed and run. Signal will then detect that Play isn't available and notify the user that the WebSocket protocol can be used for notifications instead.
This method grants Signal the Alarms and reminders permission, allowing it to run in the background as a service. This will spawn a persistent notification, as mandated by Android for all background services. You can choose to minimize or block this notification without impacting the background service or incoming message notifications.