Slow iMac Retina 4K (2017)

Hey there!

Here are some things I noticed from the report:

ESET

Be sure to remove ESET: [KB3239] How do I uninstall or reinstall ESET Cyber Security or ESET Cyber Security Pro. Third-party security utilities aren't needed on macOS, and can cause performance issues.

Hard disk

Your USB 3-equipped Mac with a hard disk can have improved system performance by connecting to an external solid-state drive (also known as an SSD). An external SSD as a startup disk can give your Mac additional performance for system responsiveness, apps, startup, and more.

To learn more, see: Use an external SSD as your startup disk … - Apple Community.

-Jack

The base model 21.5" iMac's were aimed at light users wanting to surf the web and do light native macOS tasks.

They came from the factory with a really slow 5400 RPM SATA 3 HDD.

The HDD is down from approximately 100 MB/s to 42 MB/s Read and 34 MB/s Write.

Plus the RAM is not user upgradable.

Heavy resource App's like Google Chrome, Team and Zoom can easily over-whelm these low end iMac's.

Generally these 21.5" models work well in the beginning for light users. Problem is that over time, light users become more demanding by adding third-party app's and doing more demanding things.

Yes... while using an External SSD as the Startup Disk will help a lot.

see > Use an external SSD as your startup disk … - Apple Community

The other problem, is that this iMac has a base model Processor and RAM limitations, which should also be taken into to account. In other words, if the user has moved beyond a light user doing basic task, then it is best to consider moving the user up to a more powerful system.

The real question is why should the performance degrade so much over time? Would a restore to the original (as purchased) configuration revert to original performance?

Adding a little to Jack19's excellent suggestions ... one reason the performance can degrade is that as the operating system was updated, the internal hard drive was converted from HFS+ to APFS format (this is mandated and automatic after Mojave). APFS with hard drives like this one is very slow, as APFS is optimized for SSDs. I replaced an internal HDD with an SSD for a 2015 iMac on Monterey and it felt like it was more than 10x faster with just that change.

A second issue is the very slow 30 MB/s - 40 MB/s speed measured with the hard drive in the report. It should be over 100 MB/s. Something is wrong there, it could well be that the hard drive is starting to fail. This can be researched further, but it doesn't matter, even a well functioning HDD runs poorly with APFS.

On top of this, antivirus programs check EVERYTHING, every read and every write to the disk. This can make an unbearably slow hard drive slow to be slower than slow.

So for one reason or another, your colleague should follow Jack19's suggestion, uninstall ALL antivirus and move to an SSD.