Apologies if someone made a similar point earlier in the thread as I haven’t read past the first few posts. I’m calling ******** on this from Apple. I admit this is only a rough approximation but I just laid 5 sheets of 20# paper which are 0.004” thick (via caliper measurement) or just ever so slightly thicker than 0.1 mm, and had no issues with it closing flat on my 2018 iPad Pro 12.9 LTE model. Using 8 sheets resulted in only a very slight gap but nothing that would prevent me from using the keyboard. The weight of the iPad folding down on top keeps it firmly closed just as it normally would.