The Trek Mino Link is a feature of the Fuel EX. It lets you raise or lower the bottom bracket depending on whether you prefer fewer pedal strikes or a lower center of gravity. Trek says: "Mino Link lets you quickly and easily make small geometry adjustments to suit your riding style or terrain."
As of Sept 2021 Trek's Mino Link video claims you can even swap your geometry on the trail.
I am here to tell you that you we would be insane to touch the Mino Link over dirt. If you're going to mess with the Mino Link do it over light carpet so you can see what falls out and pick it up -- especially the critical spacer/washer. A sterile environment would be nice.
The 2021 Mino Link is a mediocre idea poorly executed. (The YouTube videos I've seen describe an earlier version that the nut and the bolt, I can't speak to that design.) That doesn't mean you should avoid the Fuel EX -- I like mine. It does mean you should treat the Mino Link very cautiously. If you aren't mechanically inclined have your local shop swap it. If you are then do it over that light carpet. Check that it's secure each time you ride (I do before and after).
The problem is the washer:
SUSPENSION PART GENERIC WASHER 10 X 16 X 3.0 Item: 601479594559
Those two black washers fit are supposed to fit on the inside of the bearing race shown below. The race that's scarred up because the washer fell out when I was adjusting the Mino Lake and it took weeks for me to figure out what had happened: