Snaps that use the kde-neon extension use the host's xdg-desktop-portal implementation.
However, FileChooser dialogs (open & save) open behind the application window because Qt sends the application's window id in the wrong format (dec instead of hex).
The upstream patch correcting this problem: https://github.com/qt/qtbase/commit/acaabc9108dfe75530960cf8e3ec4f3602cd82e0.patch
I guess this would need to be added in https://invent.kde.org/neon/qt/qtbase/-/tree/Neon/release/debian/patches, but I lack the time and skills to test building a deb with this patch to create a PR.
STEPS TO REPRODUCE
1. Run any snap that uses kde-neon
2. Open file dialog
The file dialog opens out of focus in the background (at least on Gnome)
The file dialog should open in the foreground, as it is the case with Gtk applications.
I created a PR: https://invent.kde.org/neon/qt/qtbase/-/merge_requests/3
This was fixed with https://invent.kde.org/neon/qt/qtbase/-/commit/3043f743331d474b12440bfe2eb467e44dfbb3ea
kde-frameworks-5-qt-5-15-3-core20 revision 7 has hit stable and solves the issue for kde-neon snaps.
Please contribute this patch to Qt5PatchCollection next time so everyone will benefit, not just Neon.
Issue tracker: https://invent.kde.org/qt/backports-tracker/-/issues/306