macOS v11.1 Big Sur iCloud drive one way syncing issue, files from elsewhere register but files added (drag/drop via finder) stuck on upload

I have this exact problem. I have studied it at length and the issue is:

*Files* on my *MacBook Pro* that are *created or updated* do not sync to the cloud. Change any one of the highlighted terms and it works. Folders work anywhere, deletes work anywhere, and creates and changes anywhere except my MacBook Pro work (including appearing on the MacBook Pro).

But here's the fun part. I first experienced this on a 2016 MacBook Pro and got so sick of the problem and Apple failing to do anything about it, and also saying they tried to contact me without actually doing so* that I sold the laptop and got an iPad Pro. Then the M1 MacBook Pro was launched and I couldn't resist. I sold the iPad Pro, got a brand new MacBook Pro and it has *the same problem* as the old one! Better still, the 2018 Mac mini I have works perfectly fine. Did when I had the old laptop and does now.

I have raised it with Apple again and it is currently with engineering. Who have had nothing to say for 3 weeks. And this is exactly how it went last time — 3-4 week wait, followed by my asking for an update and then they'd make me collect more logs, usually in a slightly different way, then 3-4 weeks of waiting... repeat. At the point I gave up it had been 4 months.

After the problem surviving complete wipes of the (2016) laptop and fresh installs of both Catalina and High Sierra, I tried to insist the problem must be in the cloud but was told not to jump to conclusions. Now it has survived a gap of 9 months and a whole separate piece of hardware on different technology and different operating system.

I really think it's in the cloud!

*A senior adviser I spoke to this time told me that there is an "old" way of calling out of the US to other countries where the phone rings on their end but does not connect to the customer, so they think they didn't get an answer, but they're doing the call wrong. Why this is a known problem among some advisers and still happens a year later is beyond me.