Turns out, the package installer for libusb and probably the sane.d installer package as well, are outdated versions that do not run well on MacOS Catalina.
Thanks go out to Jeff Stearns for directing my attention to that.
I included these package installers out of convenience because they do not require brew to install, but I did not check the versions against the official projects. Basically these are the same installer packages I used when trying Twainsane. But as these are quite old and do not run on newer MacOS instances, my advise for installing Scanity is to use Brew to install the latest and greatest versions of libusb and sane.d and not the included package installers.
Scanity itself is completely version agnostic regarding libusb or sane.d and should run fine until Apple pulls the plug on Intel binaries or drastically alters the menubar system. That's when we'll need a Scanity 2 I imagine.
I have thought about it and decided to leave the zip with the old installer packages up for instances where people might want to use older MacOS versions and have trouble with using Brew, but for relatively new machines, use brew to install LibUSB and Sane.d and then drag the scanity app to applications.
If the options from the pulldown menu do not work, use "show package contents" and move the Scanity.app and other .app files outside the package. Calvin Walden found this problem and subsequent solution. In possible future versions, this will work better.