recently noticed my 2012 imac gets very hot while working remotely. Is this common?

Welcome!

What exactly does "while working remotely"entail? I've found video conferencing with either Zoom or Webex runs my 2017 5K iMac's and my Macbook Pro's temps up to about the same temps as games with moderate graphics do.

Before looking for software fixes, look at your iMac's physical condition and how it interacts with things in, around, and on your workstation.

1) Are the air intake vents on the bottom of the case clean and unobstructed?

2) Is there anything at all between those vents and your work surface? You must maintain the distance of about 2.8 inches. Stacking papers and other detritus of work between the vents and the desk surface can raise temps. I almost learned that the hard way when my son slid a stack of CD sleeves under my last iMac.

3) The hot air exhaust vent is on the back of the iMac's case under the stand attachment point. Its less-than-brilliant placement must be respected. While remotely investigating an overheating complaint here, I was able to reproduce the issue by tipping my case fully forward on its stand. The end user had his iMac set well above his eye-line and tipped fully down. That pinching between against the stand partially occluded the exhaust and ran temps up very fast.

Now software issues:

1) ANY anti-virus or so-called "cleaning" scams....er apps will run up the temps.

2) Google Chrome tends to run hot.

3) Watching streaming video creates the same load as a video conference. Lots happening inside inside the computer with any video as it all has to be decoded.

Remember the Mac OS uses sensors on the logic board to detect and protect agaist overheating. In newer Macs the processor may clock back under high temps until thigns cool. If temps are too high, the computer does a safety shut doawm.

What fan control app were you looking at? Some may not run under os 10.15.