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I believe Jack Dorsey (founder of Twitter) is at least a part time user. He was quite interested in the GrapheneOS project a couple years ago and if I remember correctly he donated $1 million at the time. But I believe he uses an iPhone as his daily driver. That is what most ppl see him carrying and I believe his nostr clients of choice used to be iOS specific.
So I think he's a huge fan of the project as he is very interested in security/privacy/freedom tech, but I'm guessing it doesn't work for his daily workflow.