Well, if you are asking about an "ineligible" file that you are trying to load onto iCloud Drive, the iCloud Drive documentation is pretty specific about what that means:
You can store any type of file in iCloud Drive, as long as it's less than 50GB in size and you don't exceed your iCloud storage limit. That means you can keep all of your work documents, school projects, presentations, and more up to date across all of your devices. Learn more about managing your iCloud storage.
You shouldn't store app folders, libraries, or .tmp files in iCloud Drive.
Here's the link: iCloud Drive FAQ - Apple Support
The symbols for iCloud Drive were explained above, but here they are again:
iCloud Drive Symbols
A cloud by itself just means that the item is only in iCloud, so if you were to disconnect from Wifi and go to your iCloud Drive folder, you would not be able to open any items with a plain cloud next to them
A cloud with a down arrow, means it it in the process of downloading to your local drive
A cloud with several slashes across it means that it is trying to connect to the iCloud server
A cloud with a lightning bolt means that you are currently disconnected from the iCloud server
A cloud with a single slash appears to mean that the item is ineligible and cannot be added to iCloud Drive because it does not meet one of the criteria for iCloud Drive files:
If you have other specific questions, please clearly state what they are and we will try to help.
GB