Have you ever put a professional on hold?

Yes.

Telemarketers I have sometimes done much worse to, such as 3-way dialing them to other numbers, or putting them on hold with recordings desired to torture and/or insult telemarketers,

That’s what the mute button on the phone is for. I can go to the bathroom, hit mute, take care of my business, flush, & then hit unmute. IF they ask a Q that requires a reply, I hit the unmute to answer their Q & then mute again so I can continue my business. I’ve NEVER had anyone ask me what I’m doing!!!

Used to do it all the time where I worked 50 years ago. We would often get a call for a person in our group that was working on a question / problem.
We would get back on the phone once a minute or so to let the person the other end know the the person they were calling would be with them shortly.

Telemarketers while I go get my whistle. (when it is not s recording)