Hi Pauline,
A few things to try:
1. Turn off "Hardware Acceleration" in the Zoom video settings menu
2. Make sure you are on a Wired Ethernet internet connection with as many applications CLOSED as you can. Try to only keep open the essential apps you need for the Zoom session.
3. When ScreenSharing in Zoom, take a look at all of the sharing options including the advanced options and try sharing only the individual application window (such as Word) rather than your entire desktop.
4. Ask the viewer(s) that reported a blurry share if they are on a stable internet connection.
5. Check the the resolution setting of your computer monitor is at least 1920x1080 or higher.
Hope this helps you on your way.
-Jesse