Whoa, you can now search clipboard history. Go to Spotlight Search, Command+4. You'll get a list of entries, each with a copy button, and is searchable. Even shows the app it was copied in.
Either way, I think it is better to not copy passwords to the clipboard or the selection, but store and transfer them via password-manager/browser/etc APIs.
And seriously, managers like 1Password clear the clipboard after some time. I would guess that there’s some clipboard API that allows managers to exclude copied passwords from being permanently added to the history.
Still, there are pieces of data that one might not want to store in such unobvious place as clipboard history so it’s good to know about it.
I use KeePassXC which does empty the keyboard after a few seconds. But keeping history seems like a breaking change to the social (if not technical) contract of the OS' clipboard API.