If you and everyone you talk to are hosted on servers you trust, down to the physical provider, yes.
EDIT: if the person you're talking to is hosted on Google, Google has all the metadata. Even if one person is hosted on Google and is part of a room you're in, Google has all the metadata in that room.
In 2022 e2ee is the standard for messages but not metadata, and unfortunately Matrix doesn't tackle it, so no, you can't expect 100% privacy.
But the backend of Signal doesn't store who talks to who, so Amazon can't have that information. It also doesn't store what groups exist and who is part of it.
EDIT: if the person you're talking to is hosted on Google, Google has all the metadata. Even if one person is hosted on Google and is part of a room you're in, Google has all the metadata in that room.
In 2022 e2ee is the standard for messages but not metadata, and unfortunately Matrix doesn't tackle it, so no, you can't expect 100% privacy.