Mostly, I just want to be able to copy/paste passwords and then delete them from the clipboard. It was concerning when I would delete the contents of my clipboard and the next day my password was back there again.

Looks like it was the solution for me. You can disable clipboard sharing completely, or disable the automatic sharing if you want to still be able to share when you need to.

I do use KDEConnect.

I didn’t consider that. It may be syncing my clipboard to my phone and back.

Is there an option to send the clipboard contents without permanently sharing the clipboard?

This doesn’t help me. It’s specific to keepass and is user error in using the clipboard to copy instead of keepass’s copy feature.

My case may very well be user error, but I can’t find a solution for it. It seems to keep a history of the last thing copied regardless of what I choose.