iMac Retina 5K 2020 suddenly running hot

My 2020 iMac is suddenly running hot. Photos won't sync - it says "waiting for computer to cool down" and I suddenly hear the fan running - it was not noticeable before. I rebooted and got the same results. The vents are clear, the monitor stands on my desk and is not blocked. Nothing has changed except for adding a paid version of Malwarebytes about six months ago (I had the free version forever and just ran it manually). Would that be causing the problem? if not, any suggestions for getting the computer to cool down? Thanks