Typically, reports of slow 21.5-inch iMacs made between 2012 and 2019 are due to the slow laptop-class mechanical hard drives Apple chose to install ing that model. Adding RAM cannot change glacial hard drive performance. But we are somewhat limited diagnostically by this forum setting. All we can offer at this point is a simple quiz:
- Is computer startup slow?
- Are big apps like CC slow to launch
- Once launched, do those big apps seem to perform normally?
Three "yes" answers suggest the infamous hard drive issue, but that is without data support.
If you want a data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days.
EtreCheck Pro is available here:
https://etrecheck.com/index
The free version will do nicely for this purpose, although the app is worthy of our financial support.
We can see hard data about drive performance, software issues and interferences, and RAM usage. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.
Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:
https://discussions.apple.com/docs/DOC-25000021
Posting the report is important. Most of the senior contributors in this forum section have reviewed thousands of EtreCheck reports and can pick up subtle problems you as a new use can miss.
We would be remiss if we start telling what to do without data backing us up.