I created a new account as you said above, copied all my old user files (in the ".000" folder as above) into this new account, and well...not too good
I've had my PC running in this configuration for about 3 years and installed quite a number of programs, including all applicable updates, over that time. I guess you'd call me an advanced user, having been in this game for many years, and using my PC for
non-professional audio production, video editing etc. With this, many of my programs have been specifically configured with various paths - that took months/years to fine-tune!! Before the 1903 update a couple of days ago, my PC was performing well. After
this update well, not so good. My taskbar jumplists have disappeared, my (stardock) desktop fences have disappeared. Paths are wrong. Etc etc.
The 1903 update is not working for me and I'd suggest that the scope of this 'issue' extends down to even those who use their PC's for surfing only.
Update: I've managed to roll back to the version before 1903 and it was a painless and pretty fast process, so thanks due to MS for that.
Anyway, thanks for your suggestions Dave.