2017 iMac + MacMINI

Thanks for the report. First you have a base model 2017 21.5" iMac which was designed to do nothing more than basic e-mail and web surfing however you have installed professional grade apps on it so it has ALWAYS been slow.

Next and more importantly you have installed what most experienced users would call malware, that is the CleanMyMac app. Mac OS does not benefit in any way nor does it require ANY of the following types of third party apps:

1. Antivirus apps (more in a moment)
2. Cleaning apps
3. Security apps
4. VPN apps

You also have Microsoft Defender installed, with both CMM and Defender installed you have only succeeded in slowing down your Mac even more and getting absolutely nothing in return. Please locate the developers uninstall instructions for both CMM and Defender and follow to the letter. Then run a fresh EtreCheck report and carefully look through it to see if there is ANY evidence of either app still being installed. If they are totally gone then please restart the computer in Safe Mode and then restart normally. After you are 100% sure both are gone then it is time to buy an external SSD and use the following information to install it and use it as your boot drive. This will dramatically improve the performance of the computer. How to setup an external SSD as your startup disk. There are a variety of external SSD's in many different price ranges based on your needs. Considering a 2017 is now obsolete (it cannot run current versions of Mac OS) you may also want to consider replacing the computer with a new 24" iMac which is dramatically quicker or even a different model Mac such as a Mac mini or even a Mac Studio. Any new Mac would be a MAJOR upgrade over your current machine.

Also, note that Mac OS will run well if simply kept up-to-date and otherwise left alone. Simply ensure Mac OS is up-to-date and do a simple restart about 1x a week.

Connecting it for what purpose?? If you want to use the iMac as a display for the MM, no that will not work. Simply put, iMacs are computers they are not displays for other devices.

Your slow running iMac may have a cost effective and simple solution, however without any information about it that is guess. Please do the following:

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community It is helpful to us if you download the report to your Desktop.

After we get a report on your iMac then we can look to see if there is anything obvious that is making it slow.