On macOS Catalina, it is a bit of a trick to install since the dev is not registered with Apple, but it's not too difficult.
To get it installed on catalina, open it. choose to install for all users, and then hit cancel when you get the error about an unrecognized developer. You may need to click cancel more than once.
Open the security preference pain. Under the general tab, click "open anyway". Authenticate with your login if asked.
You should get an error message. Just quit System Preferences and reopen System Preferences. You should now be able to open the MouseZoom prefpain without any pain.