And from the screenshots posted by Atlantic today is clear that Waltz added him:

Mike Waltz: Elon Musk has tech specialists who will look into how the reporter got access/was added.

Clearly doesn't require a tech specialist.

Signal screenshot:

I see your snoot and raise you one Paw 😊

Searching (in Danish) Google Maps for the Mexican Golf today. And it's still right where I expected to find it 🤣

My two cats. Brother and sister 😻😻

Graffiti from Copenhagen cirka 2017 - don't know the name of the artist. It has since been painted over. Teletubbies - the baby in the Sun has been replaced by a drawing of Trump. Biggest baby on Earth.