why can't I download scanner apps foR Ventura MAC

Ventura installs Apple's Image Capture and Preview. Either are capable of scanning from a supported scanner. Not mentioning the make and model of the scanner here ties our hands though in helping you further.

The scanner vendor is responsible for providing current drivers and their scanning software that are compatible with macOS, and some vendors are behind in this support, or have completely abandoned older scanner support.

A third-party paid application such as VueScan Professional may support your scanner without any vendor drivers, though you should check that VueScan supports your particular scanner without any needed drivers before jumping to conclusion that it does.

You could try this app. I have used this on a Windows computer and it works great. But I have not used it on my mac. It is free:

https://www.naps2.com/

Secondly, if you'd like to find others, perform a google search for "open source scanner software for macOS"