You can download Telegram and many forked clients from F-Droid. All the builds are from source code, so you know the source code is up-to-date.
Any distro can have Telegram clients, both official and third-party, in their repository.
Compared to this
1. You cannot download Signal from F-Droid. You need to download it from the Google Play Store. The released source code has lagged behind the version on the Google Play store by long periods of time many times. One example was when they implemented cryptocurrency payments, pushed the update to everyone but no one could inspect the source code.
2. Signal has sent legal threats to repositories that package Signal. The repos either need to confuse users by offering the client under other package names or remove it.
3. They also send baseless threats to forks that use their server. Combined with their lack of federation, this results in people having to use multiple apps from different sources with a much larger attack surface.
4. They beg for donations in the app even though they made an app with payments and cryptocurrency integration with an obscure coin (which they were involved with and had ample opportunity to hoard before ever announcing it as a feature in Signal).
5. They claim to have privacy features that other messengers lack, but these features are based on known-to-be-broken technologies like Intel SGX.