Signal clients are released aa open source as far as I am aware and mathematics doesn't care about what regime it is developed under.
You guys will normally find me defending Telegram here but the more important point is that we should stick to the facts even if they go in favor of "the other side".
I have not to date found anything that allows me to build a client myself and subsequently actually use it. Never mind the server, which is about as opaque as they come.
This isn't about Telegram advocacy, it's about how I keep reading "Signal is so good!" even though the devs have a very bad attitude to anyone asking about reproducible builds. When they are that hostile they do not earn trust, so it is mystifying to me that people seem to love them so much.
You guys will normally find me defending Telegram here but the more important point is that we should stick to the facts even if they go in favor of "the other side".