I am also having the same problem. My iMac is also a 2020 iMac. I have a friend who has a 2017 iMac and updated to Monterey and on hers maps is running just fine. Not much to so on but it looks like maybe its specific to 2020 model of iMac.
Like the other post (from dialabrain) below says it more local. It does not appear to be very widespread. Otherwise there would be a lot of posts here and also on the AppleMaps subreddit on Reddit. But I have only seen one other post there. Have not looked at the Apple or macOS subreddit.
I am working with a Senior Advisor (she also checked and does not see it being wide spread) to find out what is wrong. She has spoken with the engineers and they had me do a screen recording and also to gather log and system files to study.
HOWEVER, it would best if you would call Apple support. When the automated system asks what system or service you are having problems with say "Maps". This should get you to a support specialist more familiar with Maps app. Then advise them what problem you are having and you can also mention that you have heard of at least one other with the same problem and that person is working with a senior advisor who has elevated the problem.
IT WOULD BE BEST if you do as it will help to have Apple aware that others are having the same problem. Maybe they have gotten some other calls about it. Not everyone will post to online forums.
But please call Apple support about the problem. The more who do the more data points for the engineers to find the problem especially if it is localized to a certain model of iMacs.