Unfortunately I also had exactly the same problem in Windows 10 21H1.
I installed the qualitative update KB5003690 in three of my computers and obtained the following results.
First computer: very long installation times, but after no problem.
Second computer: installed on the fly and appropriately updated the OS version.
Third computer (the most powerful): after installing the qualitative update KB5003690 I have had BSOD continuously, as never happened in years of Windows 10! Regardless of what I was doing, even with when the machine was resting.
Now I'm trying to remove the KB5003690 package from the third computer, but the uninstall process proceeds very slow.
Do hope well ...