Solved: For anyone struggling, make sure isoline editing under options is switched on (alt+A)

4.35 - having the same issue. As soon as I make the Cube editable I only have a Cube's polygons to edit (6 sides) and not all the polygons as is shown in the video. Ref: https://snipboard.io/4QB3f8.jpg
Using 2023.1.3