I think he meant as in “if this is the first ever GTK application you install via flatpak”. The “Installed Size” on Flathub only indicates the amount of storage the program itself will take up and doesn’t take into account the libraries it will install alongside it (installing piper via flatpak takes up 400MB on my device).

I still think it is really negligible because people usually don’t install applications that use such a variety of different graphical frameworks, and also because modern PC disk capacities are so absurdly big compared to past ones. I only have a 256GB drive and have never faced any issues regarding how much storage flatpak apps use.

If your mouse drivers allow setting the debounce timer, you can set it higher so that your system doesn’t allow the bouncing to register.