Hi,
Is my platy fish pregnant, it’s developed a black spot in belly, hiding and being chased my other fish.
To my eyes she is pregnant, if she is showing shy behavior, this can often mean that she is pregnant. If you wish all the fry to survive, you may want to separate the fish to another aqarium. Once the fries are born, keep the mother separated as there are occasions that the mother eats them and catfish and assassin snails may eat them.
Shrimp like Amano and Red cherry can’t hurt the new born fish, avoid adding ghost shrimps as much as possible. I hope she makes a successful birth!