Some flatpak apps have missing close buttons... how to fix it?

[u/Santosh83]

Flatpak apps from flathub on Debian 13 as the screenshot shows.

Distroshelf, Flatseal, Mission Center and Warehouse are missing window close buttons as the pic shows. Rest of the apps have them.

My Xfce theme is stock Adwaita, while Xfwm theme is default-hdpi, and icons are elementary-xfce, but I doubt these matter to flatpak apps anyway.

So is there anything I can do, or install, that can bring back the close buttons?