how do i upgrade ScanSnap to be able to use it with Catalina on my Mac

If you don't find a driver for you scanner that works give VueScan a try. It supports most all scanners out there. Even though my scanner's software works with Catalina I use VueScan as it is much more versatile and robust.

macOS including the latest Catalina has an App called Image Capture which can see and use most Scanners.

Go to Applications > open Image Capture and see if recognizes the SnapScan.

https://soundsupport.biz/2015/10/18/how-to-scan-using-image-capture/

You need to contact the developers to see if they have a 64 bit version that runs on Catalina.

+1 on Image Capture

I've given up on the software that comes with scanners and now use IC only. Works very well.

Scan images in Image Capture on Mac - Apple Support

ExactScan comes with drivers and many paperless office features and OCR, maybe you want to take a look: https://exactscan.com