56 / Mk3 Galaxy here.
I find most of them are a faff to fit in upright with both wheels on, as the handlebars are too tall to fit the boot opening. You can put the bike in ‘on the piss’, and then they fit.
I take front wheel off, at which point I can carry two upright by folding one seat down.
I can carry two bikes, front wheel off, diagonally across boot if the seats are slid forward a couple of notches. i Then pack bags around them.
I can carry smaller framed bikes (26″, 27.5″ 12-16″ frame) across the boot, both wheels off.
I can fit bikes in via back door, so that when the boot has a rack of 4 bikes on already, I can get two more in the back…
They are not as deep as a Mk1 or Mk2, due to back row of seats folded. I remove that back row on long journeys (8 bolts) to gain the extra 15cm or so in depth.