macOS version 13 or later is required, to download app

If Ventura is compatible with your Mac, you could upgrade to it, and then download the app.

macOS Ventura is compatible with these computers - Apple Support

To find the hardware model name and year of your computer, use About This Mac in the Apple () menu.

Building on the 2 previous posting on this matter.

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 ? 

If Yes, suggest having at least 50 GB of Empty Space on the drive.

It will allow the Full Version ( about 12.xx GB ) to download, expand and then commence to install.

If there is Third Party Security Software installed - remove it.

It will interfere with both the download and installation process.

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

Computer Qualifying for macOS 13 Ventura 

Make Time Machine Backup  before doing any upGrades 

That could not be more clear. 13 is greater than 12.6.8. The app is not intended for Monterey.