Qt flatpaks do not use system cursor theme consistently

Qt flatpak applications (confirmed in my system with Keepassxc, Nextcloud Client, Qbittorrent, ProtonUp-Qt) do not consistently use my cursor theme (currently the default -- "style" "theme" are the default ones as well).

Bibata-modern-classic is used as normal while clicking title bars and grabbing window edges to resize.

When I click on the main pane in each and every of qt flatpak apps cursor theme changes to something else:

What I did try:

1. flatpak --user override --filesystem=/usr/share/icons/:ro in a terminal - I don't have any themes and icon sets installed in my "user"
2. sudo update-alternatives --config x-cursor-theme - idea taken from the release notes of a previous Mint release. Default theme was already selected in system alternatives as default as expected.
3. Setting "partial" permissions with Flatseal, for example /user/share/themes:ro. In fact this is same with setting overrides in the command line.
4. Give permissions in Flatseal for all flatpaks to use all "system" and (just in case) "user" files. No joy.

Please note that everything works as it should on at least LMDE5 and I don't recall having to lift a finger for that.

Full system specs

thank ya 'n' good hunting!

Start by reproducing the cursor mismatch in the listed Qt Flatpak applications on the reported LMDE system, comparing title-bar and main-pane behavior. Check whether the behavior differs from LMDE5 and verify that the configured Bibata-modern-classic cursor theme is used consistently throughout each application.