88dotorg app developers never add missing futures like "push notifications"
They mostly do, but via Firebase, Which uses Google Play services
88dotorg Google Sandbox is a powerful and great option, but why not use it short time in search of not Google depending apps so you are 100% De-Google?!
You can't expect people to abandon Important apps like the ones used for Work (e.g. Microsoft Office and Google Meet), Banking, Govt-related services, etc. just because those apps use Google Play services for some functionality.