My iMac is very slow especially when printing.

We need to see what all is running, a report from this will not display any personal info...

Using EtreCheck - Apple Community

EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/

Thanks for Old Toad’s etrecheck instructions…

Slow iMac 2017 - Apple Community

Use the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts...

Hey there!

What model is your iMac, and what version of macOS are you using? The simplest way to find out is About This Mac, available by choosing About This Mac from the Apple menu  in the upper-left corner of your screen.

Also, what model is your printer? Is it connected wirelessly or wired your iMac?

-Jack