Won't let me install Photoshop

I suggest you tell us about your Mac, so we can check what you can do.To start with, what version of macOS, and how much RAM is installed? These MUST be checked before buying any app.

You need to either use a trial before purchasing to ascertain whether your device is compatible with the latest version of the software or not. You could also look at the following link to see the system requirements

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

Do mind that Adobe allows download of only the latest two versions of the software, so you can check if your computer is compatible with either CC2019 and CC2020 version. To see/install the older versions of the software see the following

https://helpx.adobe.com/download-install/using/install-previous-version.html

Also, you need to make up your mind quickly if you need to cancel your plan as you might be charged a penalty if you skip the free refund period. For refund rules, refer to the following link.
https://helpx.adobe.com/manage-account/using/creative-cloud-subscription-terms.html
-Manan

To Cancel https://helpx.adobe.com/manage-account/using/cancel-creative-cloud-subscription.html
-or Chat link https://helpx.adobe.com/contact/support.html

-click the chat icon at the bottom right of the page to open a chat session
-the chat icon looks like '3 dots inside a circle' at the lower right
-type AGENT into the chat window to connect directly to a person rather than the AI
Do be aware that Adobe's staffing is impacted by the virus, so wait times are long
.
Also: beware of answering anyone who sends you a private message
-click for more information about scammers https://tinyurl.com/10791730