CS6 Design and Web Premium install error on Mac OS Catalina

10 year old legacy software won't run on Mac Catalina, Big Sur or Monterey.  It's  time to get compatible software if you want to keep using Mac Catalina or higher.  My guess is you need a modern OS a lot more than you need decade old software.

Depending on your requirements, you have a few options. 

Photoshop Elements or Premier Elements (approx $100, no subscription needed).
https://www.adobe.com/products/photoshop-elements.html

Creative Cloud Photography Plan (approx $10/month for 12 months). Includes the following:
- Photoshop CC and Photoshop on iPad
- Lightroom on desktop, mobile and the web
- Lightroom Classic
- Portfolio website + hosting
- Spark with premium features
- Bridge
- 20 GB cloud storage (upgradable to 1 TB).
https://www.adobe.com/creativecloud/photography.html

Creative Cloud All Apps (51 + apps & services) or Single Apps Plans
https://www.adobe.com/creativecloud/plans.html

CS6 will not install on Catalina due to changes in the operating system made by Apple.

You'll either have to downgrade to Mojave or High Sierra or dual boot CS6 from an external hard drive running Mojave or High Sierra.