Thank you and yes....
You are correct, you are far from being alone with this particular problem.
From what I've read in various resources Microsoft was supposed to have addressed this particular issue in one of their cumulative updates that they have rolled out since Windows 10 was first made public.
I'm not positive that they have or if they have that everyone with this issue have been able to secure their computers in a satisfactory state where they are able to acquire said "cumulative update".
That's why I was hoping that a Clean Boot might allow you to catch up on any pending Windows 10 updates that might be out there.
We've had other threads....
Here's one
https://www.windows10forums.com/threads/critical-error-start-menu-and-cortana-arent-working.2002/
Where some folks found that booting into safe mode and then after a bit rebooting normally, provided some temporary relief from the problem, but......
It would often return after some varied period of time.
Unfortunately that did not seem to help you at all.
I am hoping that very soon when Threshold 2 is release to the public (supposedly sometime in November) that this, as well as other issues will be resolved but, again.......
In your case, with a machine that is practically unusable it may be difficult if not impossible for you to obtain the update / upgrade.