Turns out, because I cant add Flightsimulator.exe to the exceptions list (because it wants me to open a file), I have to bypass Windows defender each time I start the pc. That’s going to wear thin after a while.
Its a work around, but not wholly acceptable for an overly long time.
Seems a way to allow potential threats in when installing addons etc… so, no addons until a fix.
When you add an exclusion, 4 options pop up:
File, Folder, File Type, Process.
Choose Process
In windows seacrh bar type
powershell
right click on powershell and select run as administrator
Copy/paste to powershell window
Add-MpPreference -ExclusionProcess “C:\Program Files\WindowsApps\Microsoft.FlightSimulator_1.10.8.0_x64__8wekyb3d8bbwe\flightsimulator.exe”
(right click to paste into powershell window)
and press enter
Run game.
OK thanks.
FS is OK now after disabling Real-time protection, running FS, then re-enabling Real-time protection, running FS.
But I copy your instructions above in my list of fixes in case it crashes again.
Restart system with real-time protection on. Run game and don’t be surprised 
Better do it now.
Turn real-protection on.
Restart system and try my powershell fix.
OK:
Turned real-protection on.
Restarted system: FS crashed
Ran powershell:
And as expected, we have:
FS starts, no crash.
So I guess, when there is a fix, I can remove the exclusion by clicking Remove in pic above.
Thank you. At least I can keep real-time protection on.
Not sure what is going on: does Defender blocks FS for a valid reason?
Have you tried the new definition update for Defender that came out a few hours ago? Check Windows update for it.
You’re welcome 
Who knows.
Fun fact.
Inside microsoft.flightsimulator root app folder is file called
WTF.dll 
Good Lord!
A Microsoft product seen by Windows Defender as a threat???
What on Earth is going on? 
why not simply add the process “flightsimulator.exe” into defender’s exclusion? much easier and quicker.
What about viruses?
Better safe than sorry 
And 4 sure not quicker.
open powershell
copy/paste
enter
done 
you will still be protected of viruses if you leave Defender running. the issue here was to avoid the crash caused by yesterdays automatic updates to MS Gaming services/xbox app, which also caused the Firewall to pop up. you have to let flightsimulator.exe through the Firewall (private network).
In Defender, simply add an Exclude for the “flightsimulator.exe” process, instead of searching and then excluding MSFS complex directory name via the “exclude path” option in Defender. no need to run powershell etc etc.
I know it LOL
nope, caused by update gaming services and xbox app
yes, you’re right
I turned off real time protection and it worked well. Wow. hmm…
You can play with real-time protecion - on.
Just got a message that gaming services was updated, now the sim window opens for a few seconds and then closes.
Rolled back the C: drive to a previous backup, and the sim loads fine again.
Minutes later, the Gaming Services updates again and BAM! the sim wont load!
How do I block the Gaming Services update?
There are threads on this already.
https://forums.flightsimulator.com/t/simulator-doesnt-start-anymore-at-all/314155/262
Basically, Windows Defender was blocking it. However, new Defender definitions came out today. Check Windows update.
Microsoft updates its Defender definitions twice daily (usually morning and evening) - here in Eastern Canada.
To force the update, as mentioned go into Settings and run Windows Update.
That said, so far none of these updates (and there’s been 3-4 since the problem started) have solved the issue.
I think we have to wait for Game Services to get patched & updated.
