I am told it is possible to toggle the Outlook 2016 setting highlighted in the image below using Powershell but I am unable to determine how that is done. It is found via FIle > Account Settings > Delegate Access. Any help appreciated and many thanks.
You are not showing what you've tried. You cannot make changes to Outlook, without navigating the Outlook object model. The same thing goes for any Office product. You need to fully understand the OM/API/Registry Settings for the target product you are trying to interact with. Search for PowerShell 'outlook settings