my Mac OS Catalina won't show or find Ventura update in software update

Perhaps your Mac is not capable of running Ventura?

macOS Ventura is compatible with these computers - Apple Support

If your Mac is not on this list you can’t update to Ventura. If it is on the list and you still cannot update then see the link below.

How to download macOS - Apple Support

The Age of this computer will Govern what newer version of macOS it will Qualify to install.

Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

Does this computer appear as Listed and qualifying for an upGrade to a newer version of macOS? 

The below links will help identify which version of macOS  this computer may Qualify to run.

Computer Qualifying for macOS 13 Ventura 

How to upgrade to macOS Ventura - Apple Support (CA)

Computer Qualify for the Monterey upgrade

macOS Big Sur 11 hardware requirements

timothy ap wrote:

it is. i checked. 2017 with two fireports.

Maybe Catalina too old an OS to jump to Ventura?

then what?

You could use the link I provided to download the Ventura installer and run it.

Which Mac do you have exactly? Check Apple menu > About This Mac.

timothy ap wrote:

it is. i checked. 2017 with two fireports.

BTW, what are "fireports"?