Hi @Al Amran
Could you please check the application log recorded in Event Viewer to see if any error?
And also make sure you download the SU with correct steps(using elevated Command Prompt window (not PowerShell) as an administrator)
Sometimes the installation of SU may cause the certificate error which will lead to Can't sign in to Outlook on the web or EAC if Exchange Server OAuth certificate is expired
Here is an official document introduces about various errors we may encounter after we install CU and SU: Repair failed installations of Exchange Cumulative and Security updates
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