Yeah distributing desktop apps is a pain. I created Conveyor to solve that, see https://hydraulic.dev/

Quick feature set of interest to your project:

• It's free for open source projects.

• It's a tool not a service so you can just download+go without even needing to sign up for an account.

• It can create signed, self updating Windows, Mac and Debian packages in one go, with a single run on any chosen host platform. So you can ship from Linux to Win/Mac without having those systems.

• Fully supports code signing, delta updates, other advanced stuff.

• Creates a nice download HTML page that detects the user's OS and CPU etc.

• Simple config file syntax.

Check it out, see if you like it.

You probably haven't read the article, but the software they build is a TUI, not a Desktop GUI (in fact a big chunk of the article is how they need to fight against Flatpak and AppImage because they are designed around the assumption of a GUI).