Signal only provides a script for .deb based distros on their official website. The flatpak is currently not ideal because it stores encryption keys in plaintext.
The provided link suggests an automated installation in a Ubuntu Distrobox including automated updates. Useful for every distro that does not natively support .deb packages.
I have used sivlerblue, kinoite and bazite. Each one of them could run appimages. What are you using?
You are correct, one shouldn’t post while sick, sorry.