I have not been able to figure out what is going on for over a week now. I have been trying to pinpoint which aircraft may be causing this problem for me, but without any luck. Has anyone else had this issue? It will just hang up on the updates page that starts before the sim boots up.
Yee. There already long threads about it.
There no fix yet.
This is a link to the Support Checklist for the issue:
https://flightsimulator.zendesk.com/hc/en-us/articles/4407168022418-How-to-get-past-the-Checking-for-Updates-screen
I’ve tried everything in that guide, and it did not provide any permanent solution.
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https://forums.flightsimulator.com/t/aircraft-avionics-update-2-beta-release-notes-1-33-5-0/592560
RELEASE NOTES 1.33.5.0
- Fixed a bug where having too many installed Marketplace content would result in the game being stuck on the “Checking for Updates” screen
Looks like they are finally going to fix it!! 
i hope so. just started on mine