How to export a PDF or Google slide presentation to one image per slide
I tried this and it worked (Linux).
Make sure gs (ghostscript) is installed, export from Google slides to PDF, and then do:
gs -sDEVICE=pngalpha -r1200 -o file-%03d.png in.pdf
Source: png - How to download Google Slides as images? - Stack Overflow
This is tested and verified by me. "-r1200" will force super high resolution, you can try without it for 100x or so faster rendering.
There also seems to be a way to script image export directly from inside Google Slides, se discussion at the above link.