For roughly 25 years I've told folks looking to run GtkRadiant on Linux to download the source and build it themselves. Last week this finally changed, and users now have the option to install an official GtkRadiant release from Flathub.
The source code for GtkRadiant is very old and hardly evolves anymore. It depends on gtk2 and gtkglext, libraries that are no longer in mainline distributions and require patching in order to build on modern systems. Flatpak offers a stable SDK and runtime, I'm hoping this shields us from distribution and compiler issues in the future.
Doing feature development iteration for an app via Flatpak introduces some annoying friction. It's possible to work with a local checkout of the source at least, but I have not found a way to do incremental rebuilds .. please comment on this post if you have a solution!
Looking at development workflows based on distrobox for instance could be a great direction to follow in order to improve this. But for now, the insulation we get from distro variations is well worth it.