Google Slides – How to Make Presentation Widescreen

Unfortunately page numbers in Presentations hasn't been implemented yet.

We don't currently support master slide functionality, so you'll need to insert numbers and logos manually.

Source

Its likely that i will be in the future - but no idea when.

Someone on another forum suggested a workaround by using the features built into Adobe Acrobat to add the page numbers (Open the document in acrobat, open the tools menu, goto Pages > Header and Footer > Add Footer/Header)

It is can be solved exactly like other question: How to show PowerPoint presentation while seeing the notes on other computer?

In Google slide, I click present with notes. I am moving the notes window to the fake monitor. and connect the second computer to the fake monitor.

Hope it is helps.