Personally I use Flatpak for two Electron apps (VSCode and Ferdium) and one GTK+ app that was never had issues with major versions (LibreOffice). GNOME apps in my case are all installed via rpm, so my experience seems to be the opposite.
GTK broke API twice in over twenty years (2->3 and 3->4), and you can parallel-install older versions. I have never heard anyone having to install specific minor releases of GTK due to breakages in the application API (theming is a different story).
I'm specifically talking about developing gnome apps. The developer documentation for Gnome uses Gnome Builder which installs a flatpack based SDK for you by default. Flatpack, it seems, is the golden path to create Gnome apps.
That's just because it lets the developer control the distribution of the app without having to find packagers in at least four distros (Fedora, Debian, OpenSUSE, Arch). Using Flatpak for the GNOME libraries is a design choice for Flatpak itself and applies to KDE apps as well.
GTK broke API twice in over twenty years (2->3 and 3->4), and you can parallel-install older versions. I have never heard anyone having to install specific minor releases of GTK due to breakages in the application API (theming is a different story).