You want to customize the user interface of the Outlook Add-In client side by hiding fields or buttons. However you cannot find an option for that.
SAP Cloud for Customer
The UI of the Outlook Add-In client-side cannot be customized. Both Ribbon and Side panel cannot be modified.
This is the standard behavior of the system.
An alternative option may be to check the SAP Customer Influencer Site to submit an idea at Influence Portal.
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SAP Cloud for Customer add-ins all versions ; SAP Cloud for Customer core applications all versions