MATRIX messenger has been shut down by a law enforcement Operation Passionflower. This is not to be confused with Matrix protocol. MATRIX is similar to Sky ECC and EncroChat.
The press release by Europol only mentions that “innovative technology” was used to intercept and decrypt messages. In three months law enforcement tracked 2.3 million messages. Dutch investigators first found MATRIX on the phone of the criminal convicted for the 2021 murder of a Dutch journalist. According to BleepingComputer, the service had about 8,000 user accounts, each paying between $1,350 and $1,700 in cryptocurrency for a Google Pixel-based phone and a six-month subscription. Also, they created a nice operation-passionflower.com page.