So I saw this thread:
https://communities.bentley.com/communities/other_communities/licensing_cloud_and_web_services/f/forum/229320/what-is-going-on-with-the-connection-client-is-there-a-conflict-with-a-recent-windows10-update-or-what
It appears that an optional update caused Bentley to use 100% of a user's CPU. Fixed by uninstalling and avoiding that optional update. However, a new update, KB5013942, is not optional and appears to contain the same things from the optional update that caused Bentley to brick computers.
This seems like a MASSIVE issue. I think the update just came out yesterday or today but it has the potential to leave every computer on our network crippled if our users unsuspectingly install this Windows update. Is Bentley working on a solution to this? Seems huge. The issue isn't Windows updates. They aren't going to revise their updates to be compatible with Bentley Connect Client. I'm assuming the client will need to be repaired.
All of the original post is correct. I would like to add that it is not just Bentley suffering from this update - ArcGIS Pro is also suffering. (This does not shift any blame or responsibility. Security updates which change APIs are a common, known aspect of Windows software maintenance.)
I highly suspect that KB5011831 (and its related rollup, KB5013942) alter the routine that is used to invoke an IE/Edge WebView component. This would make sense, as the update breaks the login phase for both CONNECTION and ArcGIS Pro. If it's not this, then it is some other issue related to threading, as the CONNECTION process hangs at a call to RtlThreadStart, a primitive thread creation call in ntdll.dll which some higher level library would be calling to invoke a thread.
I haven't had much luck coordinating with support, but if a Bentley engineer would like to reach out to me for some boots-on-ground coordination, please feel free - I'd be happy to help if I can.