Can't activate CS6 - maximum devices

Did you deactivate Creative Suite from your previously installed devices first?

- https://helpx.adobe.com/download-install/kb/activate-deactivate-products.html
- https://helpx.adobe.com/download-install/kb/activation-deactivation-help.html

That's critically important because your individual license has a strict 2 time activation limit. Remote deactivation of Creative Suite is not possible. It's too old.

If the old devices are dead or no longer in your possession, you're stuck. You won't be allowed to activate CS on another device.

Given it's advanced age and lack of support, CS6 may or may not work on new equipment & operating systems.  Good luck.

MODERN OPTIONS:
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FREE Acrobat Reader -- view, comment, print & sign PDF.
https://www.adobe.com/acrobat/pdf-reader.html

Paid Acrobat Pro -- the complete solution for creating and saving PDF.
https://www.adobe.com/acrobat/acrobat-pro.html

Photoshop Elements or Premiere Elements (3 year license, no subscription needed).
https://www.adobe.com/products/photoshop-elements.html

Creative Cloud Photography (Annual & Monthly plan options). Includes the following:
- Photoshop CC and Photoshop on iPad
- Camera Raw
- Lightroom on desktop, mobile and the web
- Lightroom Classic
- Portfolio website + hosting
https://www.adobe.com/creativecloud/photography.html

Creative Cloud Bundles & Single App Plans for mobile, web & desktops
https://www.adobe.com/creativecloud/plans.html

you have to deactivate using a computer that has an activation.  that computer must have an updated default browser and updated os.

I think you are out of luck. See the following discussion

https://community.adobe.com/t5/photoshop-ecosystem-discussions/windows-cs6-serial-number-already-in-use-by-maximum-of-two-computers/td-p/14823620

-Manan