I think the 1X and 2X designation is how the dropper trigger is mounted. the 1X trigger goes on the left side where a left shifter would go if you don't have a left shifter (assuming you're riding a single chainring up front). the 1X trigger usually look and feel just like a left shifter paddle that swings horizontally, parallel to the grip. the 2X trigger goes next to your shifter and can probably go on the right or left. the 2X triggers usually operate vertically, perpendicular to the grip. it might be possible to fit a 1X trigger next to or under a shifter as well, but that will make things crowded fast.

if your seat tube is 31.6 and the seatpost is 31.6, then it will fit. the more complicated question is: will the post go deep enough into your seat tube for your seat to go low enough for your legs when the post is fully extended? you'll have to measure what the maximum seatpost insertion is on that particular frame, which is different on each bike model and size. if inserting the seatpost all the way into the frame until it bottoms out on something inside the seat tube (a kink in the tube, a butt in the tube, or a water bottle mounting hole most often) results in a post that is too high for your to pedal comfortably, you'll want a seatpost with less drop (travel). this is more likely a problem for shorter riders. If you're tall, you need to make sure the post is long enough for you. tall riders can also use a post with more travel than shorter folks on most bikes.

it's possible to just release the post so it goes down a little but it's not advisable.