My Zoom screen is no longer sharing on my Mac
Have you checked that zoom has the right permissions?
Open Preferences &gt; Security &amp; Privacy &gt; Screen Recording and check that zoom.us.app is allowed to record your screen. 
Also check on Preferences &gt; Security &amp; Privacy &gt; Full Disk Access an allow zoom.us.app access. 
Lastly, check Preferences &gt; Security &amp; Privacy &gt; Files and Folders and check that zoom.us.app has access to the download folder (presumably to receive files).

I don't know if allowing only access to this folder and then moving the files you want to share there may allow you to send and receive without allowing Full Disk Access that seems excessive.