I was wondering if the back rest goes totally upright?
No, almost no lighter pushchair will have its back Totally, and by totally I assume 90 degrees straight seatback. It is not physically possible to make so that it would be also stable, compact / foldable right, etc. This one is not too slanted, but it is certainly not very very upright. The angle could be about 100 degrees when you pull the strap as much as you can.
P.S. Really, very few strollers have a totally upright seat, if any. From those, it is usually the reversible stroller models that also have a smaller seat space and are bulkier overall.