What printer works with an iMac 12.3.1?

Welcome to the Apple Support Communities.

Here are the printers that Apple sells that are compatible: Printers & Scanners - All Accessories - Apple. To set it up, see: Add a printer to your printer list so you can use it on Mac - Apple Support.

If you'd like, we could also try to figure out why you're existing printer isn't working. To start, let us know the manufacturer and model.

Jack

Let's see what is installed on your system that may be causing the problem. 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

There are hundreds that are available, selecting one would be based on your needs. As you don't say what your printing needs are we cannot recommend anything nor would we. You need to determine what your needs are then narrow down the printers that come closest to your needs until you have located the "one."