There is more general support being added for this in Wayland, so it’s not KDE-specific anymore.
wl-copy recently got a --sensitive flag which should automagically work with anything built on wl-paste --watch
(See: https://github.com/bugaevc/wl-clipboard/releases/tag/v2.3.0, sorry only allowed one link as a new signup.)
They also support the x-kde-passwordManagerHint=secret mime type, so implementing it this way should enable this functionality in many clipboard managers.
Related implementation discussion here which may be helpful for Bitwarden devs: Support `--secret` flag setting `x-kde-passwordManagerHint` · Issue #177 · bugaevc/wl-clipboard · GitHub