(TL;DR: Resolved by enabling Windows Event Log.)
Attempting to open Microsoft Office apps like Word or Excel resulted in a "Sign in to set up Office" window; attempting to sign in produced a "We are unable to connect right now. Please check your network and try again later." error message.
CBBG1000 mentioned encountering the same error when "connecting from Outlook Client to O365 Exchange servers via a VPN connection over Juniper Pulse" and working around it by "restarting the NlaSvc service" (which I assumed referred to "Network Location Awareness"); however, attempting to start the service via the services.msc GUI returned:
Windows could not start the Network Location Awareness service on Local Computer.
Error 1068: The dependency service or group failed to start.
Right clicked "Network Location Awareness" → Properties → Dependencies to discover the following required services:
Checked all five services; Windows Event Log had been disabled. Enabled, started, and tried signing in to Microsoft 365 again - success.
/windows | Aug 03, 2022