Newly setup Mac cannot access iCloud account

Several days ago, I resurrected a 2011 MacBookAir that had been completely erased. Reinstalled Catalina from online and it seems to be working normally...except:

I set up iCloud with the same Apple Account that I use on all other devices (Macs, iPads, iPhone,) all of which can access everything in my iCloud account. The account has about 98 GB of data.

I added a QuickBooks backup to the iCloud Desktop file with the MacBookAir, but now 3 days later the MacBookAir can't access anything else in iCloud and the iCloud account I access with everything else does NOT contain the QB backup I added with the MacBookAir.

The only thing I can think of is that it will take quite a while for the MacBookAir to "sync" with the iCloud contents. It has not been on and connected to the internet but I am going to leave it on and connected for days if necessary.

How long would it take to sync the 98 GB of data? I have fiberoptic internet with download and upload speeds of about 600 mbps.

Or am I missing something else?