You can add slide numbers to individual slides or your entire deck. There are two ways to add slide numbers. Select one or multiple slides and either:
Open the quick menu and start typing "Toggle slide number"
Open the Design panel and toggle Slide number on
The slide numbers are grey and will appear in the bottom-right corner. If you are on the Starter plan, the Pitch logo in the PDF exports will move to the bottom left-hand corner of your presentation.