After the windows upgrade few cases WMI RS integration will be corrupted, during that time we get the error "Unable to connect to the Report Server "
Solution :
Based on the SQL Server Version the MOF file will be located in different locations, in our case it was on D drive.
1. Open CMD prompt with elevated privileges
2. Run below command
mofcomp "D:\SQL Server Files\MSRS13.MSSQLSERVER\Reporting Services\ReportServer\bin\\reportingservices.mof"
=============== This will fix the issue =================