IIRC, they do forbid third-party clients from their network. You can build it from source, but you won’t be able to connect to production Signal servers.
Third-party clients would not necessarily be a bad thing. Signal has limited resources, and as such has to cut corners. I for one would love a native desktop client that’s not Electron bloatware.
Murdering your wife is one of those things that, no matter what else you achieve in your life, people will say “there goes Hans the wife murderer”. Even if you only ever murdered one wife and have shown no signs of making a habit of it.