The issue is happening on a terminal server Windows Server 2016.
Users' emails are hosted in Business Google Workspace.
Users' Outlook profiles are created with Google Workspace Sync.
Over the last months users complain that the server is slow in around 2-3 hours after working day start.
Server restart helps for few hours and then performance degrades again.
Below is the screenshot of Resource Monitor's Disk tab.
If anyone ever faced with something similar please advise what might generate PID 4 (on the screenshot) high disk activity.