Why cant you pinch hit with Ohtani?

Makes no sense. You would have to bring him in to get the last out of the inning prior to your next turn to hit to be able to get him in a pinch hitter spot. I dont like pitching with him (gold card), why should I be forced to?

they cant fix simple stuff dont expect ohtani to be usable the way he should for another 3 years

You should be able to scroll down into your pitchers when selecting a pinch hitter. If you don’t replace him on the bases he WILL be in the mound to start the next inning and have to face hitters.

Starting pitchers arent listed to be able to bring in. Only RP and CP.

You can. You just have to keep scrolling down past your hitters and you’ll find him listed as a SP.
Also, make sure you have a reliever warming up before the inning is over - and to prevent Shohei from going to the mound, either pinch run for him if he gets on base, or schedule your reliever to “come into the game.” Otherwise Shohei will come into pitch.