What does exclamation point in Cloud Icon mean?

See the following from Get file, folder, and disk information on Mac - Apple Support

Out of Space: The Out of Space status icon  indicates that the folder or file can’t be stored in iCloud because there isn’t enough iCloud storage.

Carol in Chicago wrote:

Are you sure you even want this folder? Fonts removed a year ago? I don't have any folder on my Mac which includes the name "fonts removed." How important could it be?

Sometimes you can get an out of memory signal when the computer doesn't know what to do and just starts running around in circles.

Have you tried dragging the folder outside of iCloud--directly to your user's folder, maybe? What happens then?

What happens if you just trash it?

• If font is removed how to put back in the font book .

1. Close all apps , create a folder on an empty desktop right click on an empty desktop click on new folder .
2. Click on Go , then Go to folder and type ~/Library open folder fonts ( removed ) , select fonts ( use keys on the keyboard command and A ) , copy it ( command and C) 
3. Open the new folder on desktop , press ( command and V ) , removed fonts will be copied into this folder .
4. Open font book via spotlight on top menu bar , click on add fonts or you can do in a different way , open font book & click on plus sign .
5. Deleted fonts will be transferred to its original place .

See the article Create and manage font collections and libraries in Font Book on Mac - Apple Support

Note : you have moved ( dragged and dropped this folder ) into finder > iCloud section > documents that's the reason it is showing having an exclamation mark , this is not to be done once again drag and drop this folder to desktop and move the fonts to correct location .

See the article https://support.apple.com/en-in/guide/mac-help/mchlp1143/10.14/mac/10.14

Important: Your home folder and certain other folders can’t be renamed. It’s best not to rename or move folders that came with your Mac. Many of these folders have special uses and are necessary for your Mac to function correctly.