Last Sept I pushed the button on sync my documents to the cloud. I had a few issues early on - the sync seemed to have gremlins and want to upload everything again; an issues others on this forum have had. It worked really well and I was pleased with it. However the other day it fell into a mess and wouldn’t upload files. I have tried all the recommended step to resolve - now its a complete mess and I have turned it off. I am very busy at present but looks like I need to go to the Genius Bar to see if I can unscramble this. Disappointing of course - some observers remain wary of iCloud perhaps with justification. I have used other sync systems and never end up in the pickle I currently have. Surprisingly the internet doesn’t have a lot of troubleshooting hints. iCloud just won’t work now as it says too many folders or something like that; its got indigestion somewhere! 
I honestly expected to have issues with this feature because, against my better judgement, I enabled it shortly after release.
Maybe it’s because I don’t keep a vast number of files or maybe I’m just lucky, but so far I’ve had exactly zero issues with it. It’s truly worked as advertised.
Sucks to hear that yours has gone haywire…were you trying one of the new betas or something like that? Hopefully the Genius Bar is able to resolve the issue!
Have to say, I’m with Marius here. Even when I had to delete my whole Macintosh HD (because I downloaded the Catalina beta without a backup and it ended up breaking my Mac), I didn’t lose any data since I had all my files synced to iCloud.
They just magically appeared on my desktop again after I installed macOS Mojave from the net.
Sorry to hear that it didn’t go well for you. Sadly it shows that Apple isn’t totally there yet.
Its working flawless for me. I also enabled for many of my clients and have had no trouble.
However you do have to clean things up and organize it well after you enable it the first time.
Setting up an new Mac with iCloud files works like a charm.
Curious - have you logged out of iCloud, then log back in from that device? Give it awhile (and maybe reboot) for the background activities to do their thing…