photoshop

Can you update your Mac operating software to Mojave, Catalina or Big Sur? 

Yeah, Adobe expects customers to use the latest software, no more than 2 versions back.  CC Desktop App contains only the last 2 major release versions.

Please see the minimum system requirements for each app you intend to use:
- https://helpx.adobe.com/creative-cloud/system-requirements.html

ProDesign Tools' website has links to some older installers.  But Adobe can remove these anytime without notice.

https://prodesigntools.com/adobe-cc-2019-direct-download-links.html

Be sure to follow the VERY IMPORTANT INSTRUCTIONS or it won't work.

Hope that helps.

Hi @Juanita5CBF 

Did you look at the system requirements before you purchased a plan? 

https://support.apple.com/en-us/HT202491

You might be able to install PS 2020 instead of 2021 on macOS High Sierra.

https://helpx.adobe.com/photoshop/system-requirements/2020.html

If not, contact Adobe Customer Care:
https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 
or send a tweet to @AdobeCare for support.

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~ Jane