Comment by st_goliath

There is no such thing as an "X11 clipboard" that something can be written to. As the poster goes on to allude, X11 has a concept of a "selection" (a primary and a secondary one).

It goes roughly like this: when you select a text in a window, the X client tells the X server "I have the selection now", when you paste in another window, the client behind the other window asks "who has the selection?" and requests the selection contents from the other client, the data is then forwarded through the server. The client that claimed ownership has to properly handle some associated requests/events for the whole thing to work.

The key point is, there is no central "clipboard" style repository like on Windows, the client that does the "copy" is responsible for the data, the client that wants to "paste" has to talk to it. If I try to copy/paste and quit the source program before the paste, the data is gone. That's why modern desktop environments usually come with a dedicated daemon that immediately reacts to selection ownership changes, grabs the data for itself and then claims the selection ownership to emulate the Windows style behavior.

If we play devils advocate, it's possible the Zoom client tries to do just that, not trusting whatever desktop environment. I don't use this software, so I'm going out on a limb here, but I'd guess that the "Zoom Desktop Client" is just another browser in disguise? It might be actually Chromium or whatever underneath that does this?