What does the Creative Cloud show when you highlight installed apps. Mine shows I have CS6, CC 2014 and CC which it shows for CC 2018 version 19.1. All Apps shows all installed and addition current versions that can be installed. If you took the default install settings when you installed CC 2018 the installer would uninstall prior version of Photoshop. If you want to keep your working versions of Photoshop you need to use the advance install options and uncheck remove prior versions. IMO the should be the default setting.
If you get the new version working well for your use youcan the remove your old working version. Not a good idea Adobe may release a new update that breaks something in the current version that you use. You should always have a backup working Photoshop version installed....
Your Creative Cloud Desktop application may have a problems if the old versions are still install one your system There are only two Photoshop Launch button shown.
At one time I had versions 3, 14, 15, 16, 17, and 18 installed all had launch buttons in the desktop application and there were more in windows start for I had the 32bit and 64bir versions of CS6 and CC installed. I had to rebuild my system because of a Windows1 0 Preview build. I chose not to install CS2, CS3. CC. CC 2015, CC 2015.5 and CC 2017.
The other versions
You've hit on the perplexing thing. The older versions don't show up. Here's my "INSTALLED APPS" (jeez, Adobe, why ya' shouting?) list:
They usually show the older versions as in your screen shot. The only one they're showing is my REALLY old version (but still mine if I don't subscribe.)
Here's what's in my Applications directory:
Make sure they are still installed. CC 2018 installer would remove old versions of Photoshop CC if you did not use the advance install options and uncheck remove prior versions. If the are not you should be able to reinstall them and you old preferences may still be intact and your third party plug-in may as well. When Photoshop is install the installer does not build your preferences and does not install third party plug-ins. Uninstalling Photoshop does not remove users preferences and third party plug-ins. CC 2017 folder may still be there for in its plugins sub folder third party plug-ins are installed.... I use windows your mac install is quite like windows install tree Look in CC 2017 folders...
When trying to run version 2017, I get this error...
Photoshop CC 2017 files are still present, though. I can tell by the amount of space used.
I was mistaken in thinking they both are runnable. Both 2017 and 2018 versions of Illustrator run without error.
Guess I'll try "installing" Photoshop CC 2017 after researching the above error. Maybe that will give me the option to uninstall via the CC app.
If you want to install an older version of Photoshop I would suggest CC 2014. There is not much differences between CC 207 and CC 2018. CC 2014 has fewer bugs than both CC 2017 and CC 2018.
This problem has now been resolved. Thank goodness Adobe has the provision for installing older versions.
What I did was install the CC 2017 versions of Photoshop and Illustrator even though they were already present on my computer. The Creative Cloud app cheerfully went along with this, installing CC 2017 versions atop the existing programs. I was then able to uninstall them using Creative Cloud.