“We’re aware of reports that access to Signal has been blocked in some countries,” Signal says. If you are affected by the blocks, the company recommends turning on its censorship circumvention feature. (NetBlocks reports that this feature lets Signal “remain usable” in Russia.)
Matrix has the unfortunate problem right now where all the big clients have matrix.org set as the default homeserver. Yes, it is a decentralized and federated protocol, but I wonder how many users are registered on matrix.org vs other servers.