Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4910917.

Printed with .4 line width, no filling anywhere ans layer height of 0.24

You sould add some rubber or felt feet if you want.

You need 2 copies printed to hold the ipad.

This is for the 2018 model, 12.9"

If after printing your ipad does not fit the slot (maybe for calibration issues) you could heat the piece a bit (heat gun or hot watter) and bend the lip so it fits properly.