iMac Lagging

Without any specifics there isn't much we can do. Please do the following.

You can save you and us a lot of time and effort of playing 20 questions if you do the following:

Please navigate to the Mac App Store or 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 https://discussions.apple.com/docs/DOC-250000211

I have the same problem and have had to create 3 separate support cases with no solution still! The time the machine takes to reboot in safe mode or diagnosis mode or whatever it is the support member has me do on the computer takes too long so they schedule a call back and never call back. Tried to upload the system diagnosis report to support to send to the engineers, but it quit before upload was complete - every time! I only use Chrome and one or two Microsoft programs (Outlook, Word, Excel) and every time I toggle between apps or even just tabs on Chrome I get the spinning rainbow wheel of death. My base-model 2014 MacBook Air is faster than this piece! I'm pulling my hair out trying to figure out what the heck is wrong: do I need to use a different browser, is it my wifi, is it because its connected to One Drive??? I've wasted so many work hours because its so slow!

Same problem same request: download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Also click and read the About info to further permit full disk access.

Then we can examine the report and see if we can determine what might be causing the problem.