The server’s trustworthiness does not matter for Signal. The app is designed to work securely regardless of the server. Moreover, even if the server software is open source, you cannot be sure that they run the same code that they publish.

The server’s trustworthiness does not matter for Signal. The app is designed to work securely regardless of the server. Moreover, even if the server software is open source, you cannot be sure that they run the same code that they publish.

Older machines can be at risk from hardware flaws. But if your machine can run Windows 11, which most machines from 2019 can, you can safely use and install Linux on it. I recommend not buying a new machine that lacks official Windows 11 support even if you want to run Linux.

I would usually not be concerned about old hardware as long as it can run a modern OS I trust. This means most laptops are fine, but phones not so much.

This is not a good suggestion because even with up to date and modern operating systems, hardware vulnerabilities can often be leveraged

Security is not guaranteed by simply using linux. It may even worsen it.

https://madaidans-insecurities.github.io/linux.html

This article shows why your proposals are not secure at all:

https://madaidans-insecurities.github.io/linux.html