How do I speed up my sluggish MAC

 Download and run Etrecheck.  Copy and paste the results into your reply. 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 Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

Please read Writing an effective Apple Support Communities Question to get an idea of what we need from you in order to answer your question. All of our mind readers are out of the office indefinitely and no they are not working remotely.

In short, Macs have been in continuous production since 1984 and there are many many many versions of Mac OS since 1984. Without having specifics, we cannot answer your question.

Where are you noticing the beachball the most? What apps and under what circumstances?

I don't see any of the ususal suspects in the report. However, be aware that at the time of purchase you bought the slowest iMac that Apple offered: 8 GB of RAM and a 5400 rpm hard drive.

This is confirmed by the current read and write seed of you hard drive:

Write speed: 67 MB/s

Read speed: 63 MB/s

I noticed you have Dropbox installed and running. There have been a few posts where beach balling was the problem and when the OPs removed Dropbox it improved a lot. You might try uninstalling Dropbox and see if there's any improvement. If there is and you need a replacement give Box a try. Several posted have tried it and liked it better than Dropbox. I use neither so can't comment from experience.

You could speedup boot time, application and document opening time and document saving time by getting an external SSD, cloning your boot drive to it with Carbon Copy Cloner  and boot and run from the SSD. The read and write speeds can be increased by up to 10x over what you have now, many even more. I suggest you contact OWC (MacSales.com) customer support and see what they recommend from their many offerings that will meed your iMac capability, needs and budget.