You're part way there. The only app that can be downloaded as a .dmg from Adobe is the Creative Cloud app.
Once you install that, then you can choose to install Photoshop. Like all other titles directly from Adobe, the CC app controls all installs and uninstalls. You cannot get individual app .dmg downloads.
I did as much checking on that as I could, too. The CC app has no option to download storable .dmg images of their apps. Logging into my account on Adobe's site results in the same thing. The one and only item with a download button is the Creative Cloud controller app. All others say Open on Desktop if already on your Mac, Install if it's part of your current CC plan but not currently installed, or Free Trial / Buy if not part of your current subscription fee.