my mac desktop is super slow

Hi bbscreen,

Welcome to Apple Support Communities.

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

1. Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
2. Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities. 
3. Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
4. Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

-Jack

Notes from EtreCheck:

• Kernel Panics. Please see: If your Mac restarts and a message appears - Apple Support.
• Delete CleanMyMac. [Instructions]

Other than that, the reason your iMac is very slow is due to the 5400 rpm hard drive. Very slow. If you use an external SSD and run macOS from that, it will make your Mac 10 to 30 times faster for storage. For more info, instructions, and what external SSD to buy, please read: How to Setup and Use an External SSD as y… - Apple Community.

-Jack

Very nice. You've done well to get that report posted.

It looks like you have CleanMyMac installed. It's about as close to malware as you can get without actually being that. Use the publishers instructions and remove that from your machine. "Cleaning" apps and "speed up" apps are unnecessary on macOS. And very often they just gum things up, conflict with system software and cause problems. Get rid of ALL the CleanMyMac components.

Your startup drive is an aging 5400rpm mechanical hard disc drive. The read and write performance is in the 50-65 MB/s range. That's terribly slow. You would do yourself a world of good if you could buy an SSD drive in an external case and use that as your startup disk. I would expect a read/write speed of 250 MB/s at least which is much faster than what you have going. The HDD is a severe bottleneck to your Mac's performance.

Otherwise, things look pretty good.

After you've uninstalled al the CleanMyMac junk from the machine, head over to the MalwareBytes website https://www.malwarebytes.com and download a free copy of their utility. Use it to scan your computer for anything that might have been missed by EtreCheck.

I suspect your biggest problems are the two I've mentioned. And if that is the original HDD that the machine came with, I suspect it won't be long before it starts to have other problems. I hope you have all your data backed up. If not, do that today.

Start with an EtreCheck evaluation of your Mac.

EtreCheck is a diagnostic app that gathers and reports important debugging information about your Macintosh. It is very highly regarded and meant to be used with Apple Support Communities to help others help you troubleshoot and resolve your Mac problems.

Please navigate to EtreCheck.com and download the free version of EtreCheck. Once you’ve run the app and created your report please post it with your reply to this message. 

You must upload the full report. For instructions on how to attach your EtreCheck report to your reply, please click  How to use Add Text when posting…

We can use the EtreCheck report to look for the more obvious things that may be causing your problem and advise how to correct them.

In order to see a performance gain, the external drive must be an SSD, such as the LaCie Mobile SSD High-Performance External SSD USB-C USB 3.0 - Apple Store.

For instructions on setting it up, see: How to Setup and Use an External SSD as y… - Apple Community.

iMac was never intended to be opened by users. It must be external, and an external SSD has about 85% of the performance of adding an internal SATA SSD anyway.

-Jack