Downgrade?

OK J, you have a lot going on here, let’s pick ’em off one by one:

Your screen shot of the Creative Cloud Desktop App installer does show that Photoshop 2020 is available to you. Photoshop 2020 is version v21.2.4 shown in the screen shot, and Photoshop 2021 is v22. The version numbers don’t match up with the years because Photoshop 1.0 was released in 1990; the reason the year and version number are close enough to be confusing is that they didn’t exactly match up in 2014, when Adobe started attaching the Creative Cloud release year to the application name. Should Adobe label that screen more clearly? Yes, they should…

Adobe Creative Suite 6 cannot be installed on macOS 10.15 Catalina. The CS6 applications have too many components that don’t meet the more stringent Apple requirements in macOS 10.15 Catalina. One problem is that some components or applications are not 64-bit code.

If Photoshop 2021 (v22) is slowing down to the point where you can’t get your work done, there is nothing about your screen shots to indicate that RAM is the problem. RAM management is complex. Most importantly, a readout of low free RAM means almost nothing because of the way macOS constantly moves data between real RAM, compressed RAM, and VM. The best way to evaluate RAM is looking at Memory Pressure in Activity Monitor, because it is a more holistic number accounting for how well the entire memory system is doing. If Activity Monitor says Memory Pressure is green, RAM is not a problem. Orange would be a concern, red would be a real problem.

Because the free RAM amount is not useful and Memory Pressure is very useful, I no longer use system monitor utilities that can't tell me Memory Pressure. (I use iStat Menus, which does.)

That still leaves the question of why Photoshop 2021 is giving you problems. If you install Photoshop 2020 (v21) and the problem goes away, then there is a real problem with 2021. You might take a look through the Photoshop Feedback website where bug reports can be submitted, tallied, and discussed publicly, in case there is an existing bug report you can add info to. This forum is just a general user discussion forum, while the Photoshop Feedback site is more focused on tracking and taking votes on bug reports and feature requests, and Adobe staff actually join the comments for some reports to get more info or announce fixes.