Size up or down on gravel bike?

I'm smack bang in the middle between S and M for the Polygon Tambora A4 – Polygon Tambora A4 – Gravel Bike (height: 164cm, inseam: 77cm). I think I have pretty long legs and a small torso. I like riding more in an upright position and don't really care about going fast. Will use this bike primarily for commuting with the occasional bikepacking adventure. Should I size up or down? S is sold out so if I need to size down I'll look at another bike. Thanks