From what ive seen the phone providers are using googles backend software called “Google Jibe”

A lot of them are. But Google is not the only option. There are carriers that roll their own solution, rater than using googles white label solution. Chinese carriers are for example offering RCS under the name of 5GMessaging and they aren’t using Jibe.

Also by the fact that it doesnt work on degoogled phones you can surmise that google has the ability to disable or limit the feature on any device with google play services.

but that’s a client problem, not a server problem. There are providers in some regions who offer their own apps that still work with custom roms. It’s just the Google Messaging app that does play services attestation. Almost everyone uses this client, but it is only almost everyone.

I don’t disagree that there is some open washing going on, but that wasn’t your original claim. You stated that Google needs to approve any client and that’s just factually wrong.

No it doesn’t. It’s a federated service that’s controlled by the GSMA. Services are either provided by your phone provider or Google. As far as I know it’s not an open standard, meaning that you need a licence to develop a client. But the licencing is not controlled by Google but by the GSM Alliance (the same organisation that controls the GSM cell standard)

Will the Jolla Phone work outside Europe, can I use it e.g. in the U.S.?

Yes, we have designed the cellular band configuration to enable global traveling as much as possible, including e.g. roaming in the U.S. carrier networks.

https://commerce.jolla.com/products/jolla-phone-sep-ii-2026