It’s usually just the first bit while it indexes the photos, then immich settles down.

RCS is off-topic.

Disagree, it serves to illustrate the same kind of monopoly google has on push notifications.

UnifiedPush is not a push service, it is a distributor. It is a proxy for push services, it does not send out its own notifications.

Also, ntfy does not need to use unified push, it simply makes put or post notifications, like it does in the self-hosted version. The public instance of ntfy does use unified push, yes. For instance, I do not want my http push notifications flying around in plain text with notifications about my private services being up or down, so I don’t use one. I arrange the connectivity to my applications myself.

Here again, google has done us all a disservice by obscuring the difference.

That is correct.

However, this is a quasi-monopoly by google having quietly overwhelmed the space. Same thing for RCS messaging.

Neither push notifications nor RCS are proprietary, so there is a possibility to tear oneself from google here.

For instance, there are several free and paid push notifications services. Pushbullet is a popular paid one, not too expensive. I personally use https://ntfy.sh/, which can be self-hosted.

RCS is different because trusting the encryption keys makes RCS work, so there would have to be a critical mass of buy-in to use an alternative to google’s RCS implementation.