Is it permissible by NEC to put a (dedicated) dishwasher circuit and a (dedicated) microwave circuit on a shared neutral?
Will be running 20 amp/12 gauge line.
If allowed, I would use a double connected breaker.
Let me know if you have any more questions or see any concerns.
Thanks, Steve

This is fine. It is a typical multi-wire branch circuit and it doesn't matter if it is in the kitchen, garage, or where ever.