If you get a lot of these events (and the alert you're seeing suggests you may be) - and they prove particularly disruptive to your WiFi clients - you may prefer to stop your APs from from using the 5 GHz channels on which DFS is mandatory. If you do want to do this, instructions are here: https://documentation.meraki.com/MR/Radio_Settings/RF_Profiles
This should be avoided, if possible though, because having a greater number of available channels allows your APs to co-exist with reduced co-channel interference - and your WiFi can potentially perform a lot better. It will all depend on how frequently you see these DFS events. You can search for these specifically in the network-wide > Event log. The Meraki Support team will help you assess the DFS situation, if you raise a case.
I don't like seeing my fully functional working AP's set as amber (suggesting a more serious problem) because in the past 24hrs they automatically switched from a DFS channel to a non DFS channel. AS GreenMan says, most users will use all available channels including DFS channels to give the least channel congestion. In the event of an air ambulance flying over the building in the middle of the night for a few seconds, and my AP's on the top floor detecting it is not a problem in my book. I'd like to be able to switch off this alert from making my AP's appear as alerting, I didn't have it before and I don't want it now