Not an ideal solution, but I ended up reverting to Monteray and then computer audio sharing in Zoom worked for me. I didn't want to stay on an old OS, so I rolled the dice and reinstalled Ventura as a software update. Audio sharing is still working as I expect in Zoom. So, thankfully, I didn't need to go back to Monterey again. Unintended extra work to reinstall programs and tweak settings every day but my fingers are crossed that Zoom computer audio sharing will continue working.