"Signal is being blocked in Venezuela and Russia. The app is a popular choice for encrypted messaging and people trying to avoid government censorship, and the blocks appear to be part of a crackdown on internal dissent in both countries..."
Matrix doesn't protect metadata, which is arguably just as (if not more) important than message data. Signal by contrast does protect metadata and proper implements Perfect Forward Secrecy for all chats. I do think Signal's centralized design and phone number requirements problematic, but Signal still has many merits. Such as its massive user base for a AGPL-only project.
Citation needed. It is undisputed that the software that runs on their servers is not identical to the code they release; if they release at all because sometimes they just stop for a year, until people complain đź«