Yes, it is Necessary to install the SU Update. The security updates for Exchange Server address vulnerabilities responsibly reported by security partners and found through Microsoft’s internal processes. Although we are not aware of any active exploits in the wild, our recommendation is to install these updates immediately to protect your environment.
Please check the Known issues in the security update
And we may also encounter the issue after installing the latest SU: Can't sign in to Outlook on the web or EAC if Exchange Server OAuth certificate is expired, which caused by oauth certificate not configurd correctly.
You could also check if any error recorded in application log.
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