I can't get Ventura why???

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.

Computer Qualifying for macOS 13 Ventura 

Computer Qualify for the Monterey upgrade This is the last version of macOS this computer Qualifies to run

macOS Big Sur 11 hardware requirements

All is not lost though 😀

If the user wishes to explore the Apple Trading In option where the Value of the exiting machine could be used against the cost of a new Apple Computer 

Or Shop Refurbished Apple computers at an Apple Reduced Cost

Have used both previously and have been satisfied each time.

It simply put doesn't have the modern hardware needed.