Here is a short list of things that Play Services do:
Scan for active malware
Nearby Share
App attestation (Required for banking apps)
Encrypted backup of your data
Autofill
All push notifications
Find my device
Basic telemetry (talked about elsewhere in this thread but it’s telling Google who you are and where you are)
Even if you remove all telemetry you’d need to have the services running 24/7 in the background maintaining a socket connection to push notification services.