I am using the bitwarden desktop app on Linux/KDE, which uses arboard to manage the clipboard and noticed that passwords are stored in the KDE Klipper clipboard manager history.

This can be circumvented by adding x-kde-passwordManagerHint MIME data hint to the clipboard entry and setting it to secret, see:

https://bugs.kde.org/show_bug.cgi?id=458063

This is implemented in keepassxreboot in this PR:

https://github.com/keepassxreboot/keepassxc/pull/1969/commits

BTW the current source code of keepassxreboot also contains an implementation that prevents macosx to put secrets into the clipboard manager: https://github.com/keepassxreboot/keepassxc/blob/7bfe9065cf3a7b9e32094d965eb13a8c7fc0cc82/src/gui/Clipboard.cpp#L56 So maybe this should be part of the generic interface.