Creative Suite 5.5 Activation

Which operating system?

Legacy CS5 won't install on modern macOS beyond Mojave. It's not compatible with 64-bit systems.

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

Creative Cloud Photography Plan (Annual or Monthly plans available).
https://www.adobe.com/creativecloud/photography.html

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

Make sure your computer meets the minimum CPU & GPU requirements. Most Creative Cloud apps work on these systems, no more than 2 versions back:

• Windows 11 (64-bit) versions 23H2, 22H2; Windows 10 versions 22H2, 21H2;
• MacOS 15 (Sequoia), 14.7 (Sonoma), 13.6.7 (Ventura).

- https://helpx.adobe.com/creative-cloud/system-requirements.html
- https://helpx.adobe.com/photoshop/system-requirements.html
- https://helpx.adobe.com/photoshop/kb/photoshop-cc-gpu-card-faq.html

your newish mac supports 32 bit apps?

if so, try offline activation.  

disconnect the computer from the internet

Launch the product.

At the Serial Number Validation screen, click Having Trouble Connecting To The Internet.

Click Offline Activation and click Generate a Response Code.

Write down the Request Code.

Switch to an online computer and navigate to www.adobe.com/go/getactivated.

Click Offline Activation.

Sign in with your Adobe ID.

Enter your Request code and click Generate.

Write down the Response code.

Switch back to the offline computer.

Enter the Response Code and click Activate.