Hmm, I've had the pleasure of updating quite a few machines for the company I work in. The experience has varied wildly across systems. Our secretary still had Windows 7 running, and so did I. I updated her machine straight to 1909, she walked in on Monday and commented that it felt only the Task bar had changed, she was able to carry on working right where she left off before the weekend.
On my own workstation, that, for software compatibility reasons needed 1807, required 1,5 day of setting up, fixing broken software and as a finale, the GPU literally blew up (FirePro vapor chamber went *poof*, probably unrelated however).
So, for some people, the update is probably just fine, while others will have massive problems. That's how it's been ever since Windows 98, and probably the way it's going to be in the future.