Wrong window decorations on KeePassXC Flatpak

I am using GNOME on Bazzite. All of a sudden, starting yesterday, the KeePassXC Flatpak is no longer using Adwaita themed window decorations. It seems to be falling back to some default:

Other Qt based Flatpaks do not have this issue, e.g. Scribus, Kdenlive, and Haruna:

I tried reporting this issue on the GitHub page for the KeePassXC Flatpak and was told that this could be Flatpak KDE framework issue. I would appreciate some help diagnosing the problem so I know where to report it.

I filed a bug report before finding your thread. Here it is: https://bugs.kde.org/show_bug.cgi?id=513238