Do Not Forward Button Not Showing in Ribbon

MariaYacaman This isn't a valid advanced setting for the unified labeling client.  You'll find a list of the advanced settings for policies, here: https://docs.microsoft.com/en-us/azure/information-protection/rms-client/clientv2-admin-guide-customizations#available-advanced-settings-for-label-policies

Displaying the Do Not Forward button on the ribbon isn't supported for the unified labeling client. Going forward, all protection actions should be the outcome of a label. So for an equivalent, create a label with your choice of classification, and for the protection settings, select the option to let users assign permissions when they apply the label, and select the option "In Outlook, enforce restrictions equivalent to the Do Not Forward option"