PreviewPowerPoint · Desktop
PowerPoint: Set slide size in a modern PowerPoint pane
PowerPoint users will gain access to a modernized slide size panel with real-time preview, common presets including social media formats, and easier custom dimension entry. This is currently in preview and available to Standard Multi-Tenant environments.
Microsoft's description
Change slide size in PowerPoint from a modern task pane that keeps you in the flow of editing with real-time slide changes. Choose common slide sizes including new social media presets, or customize dimensions with a cleaner, more approachable experience.