Trump's threatened use of a never used provision in the US Constitution is very, very disturbing.

https://www.youtube.com/watch?v=NkF05D-NJMU

He knows it is going to hell and he hasn't a clue what to do and he has to smell good, so pass the buck. Not a leader but a filthy scoundrel, the destroyer of America.

Perhaps I trust the maker of the radio more than I trust the garage.
But you are of course correct, however as it doesn't actually affect me I don't feel like taking on the job of reporting it to MS.
Perhaps the OP would?

I can replicate the behavior. I just upgraded my daily driver to the new Windows 10 Creators Update. I suspended GPU processing and all other projects so that I can ensure only SETI CPU tasks are running. I also upgraded my BOINC to v7.6.33 to keep the test as similar as possible.
Note that the Windows 10 upgrade did not force Microsoft's video drivers onto my system. It left my existing Radeon Crimson suite installed.
I set my screen saver from disabled (because I don't use it) to BOINC and set the timer to 1 minute. I can see that my screen goes to the BOINC message saying it is loading the screensaver, then it dumps me back to my desktop. Tested this 4 times and the screen saver won't actually load.
I can't say that I exactly replicated the problem because I don't know if it was working on my system before the upgrade. As I said, I don't bother with the screen saver so I leave it disabled. For all I know, it may not have been working before the upgrade so I can't blame it on the upgrade yet. I decided to go over to my girlfriend's computer to test since she's still using Windows 10 Anniversary Update, and performing the same on her's (enabling the screen saver and setting it to 1 minute) seems to work as expected.
There's nothing in the BOINC Event log, nor do I see anything recent in stderrdae.txt. I even fired up procmon.exe and filtered at first for anything that began with BOINC, then after failing to note anything of importance I filtered down to any result that wasn't a success but still nothing. Finally, I filtered further for all process names of boinc.scr and results there were not a success, however I still don't see anything that sticks out as an obvious cause.

"BOINC does not start" means "boinc.exe is not in the list of running processes" (as seen in Windows Task Manager, Process Explorer, ...)
"no engaging the screen saver" does not mean BOINC is not running.
BOINC screensaver (boinc.scr + boincscr.exe) only shows some pictures, it is not really needed for the processing
("processing" is done by SETI@home applications which are started by boinc.exe)

The screen saver uses OpenGL on the videocard to show the graphics. As other Windows 10 upgrades have shown, they'll overwrite any and all user installed drivers by crap Microsoft deems more important or better than what you had. The Windows installed crap drivers don't include necessary things such as OpenGL (and for calculations on the GPU things like OpenCL and CUDA).
So always get your drivers from the manufacturer of the videocard/GPU. In your case, Nvidia and if you use the Intel GPU for driving the monitor, Intel.

Can't get it to run even after reinstall of BOINC 7.6.33

How not so, what error message or any other message do you get?