Please add the "Milestone Type Name" field to the available fields in the Timeline Advanced filters.
When filtering in Timeline, we have the ability to quick filter on Activity Type of “Milestone”, but there is no further way to filter the resulting list to a specific Milestone Type via the “Advanced Filters” option in Timeline. The “Milestone Type Name” field is not available here. The field IS available when building a report, or using rules engine as an example.