Someone (https://gitlab.gnome.org/GNOME/cheese/-/issues/52#note_913663) confirmed that the patched package ( https://launchpad.net/~apandada1/+archive/ubuntu/cheese-headerbar-buster) fixes the issue in KDE in Debian Buster 10.5.
However, this is only a workaround. Please consider applying the patch to the official Debian package for Cheese.
