why can't I down download icloud files

See a thread https://discussions.apple.com/thread/253481383

Read Use the Files app on your iPhone, iPad, or iPod touch - Apple Support

If you need help

• Update your iPhone, iPad, or iPod touch to the latest iOS, or iPadOS.
• Set up iCloud on all of your devices and turn on iCloud Drive.
• Make sure that you’re signed in to iCloud with the same Apple ID on all of your devices.
• If you want to upload, download, or share files using cellular data, open Settings, select Cellular, scroll down to iCloud Drive and any third-party cloud services you use, and turn it on for each service. 

If you don't want to access your iCloud Drive files in the Files app, you can choose to download and add only third-party cloud services instead.

I am having the same issue - everything is up to date across all devices. My new Mac and iPhone are not able to upload/sync data. Mail and internet working fine but clearly something amiss with iCloud sync. Notes aren't synching, can't download desktop files (turned off/back on), photos last synch was 3am.

Had the same issue, spoke to several engineers who weren't aware of any problems and whilst on a call with an engineer syncing starting (as if by magic... but then "icloud is magical"!). Still having icloud drive sync issues on my ipad but expect things will suddenly start working again with a little patience :-)

BTW, got cut off whilst on a call with an engineer as my problems were 'disappearing' and never got a return call (so far).