I've carried a Shield in a kydex tuckable holster made by Cooks:
https://www.cooksholsters.com/tuckable-iwb-holster/It works ok, but I have a smaller waist and a thicker chest/back so it helps hide it a bit, especially since the shirt is looser around my waist. The thin profile of the shield along with the thin kydex helps.
I much prefer OWB with cover but sometimes I can't get what I prefer.
