Hi,
Please let us know how are you testing the outlook web services? Below are my suggestions,
Test-OutlookWebServices applies to Exchange 2010 - https://learn.microsoft.com/en-us/powershell/module/exchange/test-outlookwebservices?view=exchange-ps
For Exchange 2016, try using Test-WebServicesConnectivity - https://learn.microsoft.com/en-us/powershell/module/exchange/test-webservicesconnectivity?view=exchange-ps
Also, you can create a new mailbox in exchange 2016, configure the outlook and check the EWS features like out of office, calendar free/busy,etc
Check the URL using Get-WebServicesVirtualDirectory and also the autodiscoverserviceinternaluri in Get-ClientAccessService
If the above suggestion helps, please click on "Accept Answer" and upvote it