as a user of Maccy, yes anything you put on the clipboard will be an entry in plain text. Maybe there is a way to do a 'secure' copy with Maccy but I'm not using it so I can view my passwords via the buffer.

edits: I guess this is only the case when you copy the plain-text. Seems there are event types associated with the copied target that Maccy will ignore if it believes it is a 'confidential type' Check the GitHub README