Morgan is a robot
Someone online posted their sister's reaction to Morgan in Endgame: The sister thought Morgan was a robot (version number ILU-3000). That's why Pepper is never shown interacting with her, and why the others were so uncomfortable around Tony--because no one knew how to mention he was treating a robot like his kid. Let's take a look at that conversation.
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Tony stood on the porch beside Morgan as Scott, Natasha, and Steve headed to the car. Tony said, "You have to understand. I have to protect my daughter."
Morgan stood surprisingly still for a child her age, but then her head jerked and she was waving and saying, "Bye! Bye! Bye!"
All three heroes looked in the rearview mirror as Steve turned onto the lane that took them away from Tony's private lakeside paradise.
Scott broke the silence first. He said, "I think she glitched a bit, at the end there."
He sat back in his seat and continued, "Still, it's incredible technology. I wouldn't have believed it was possible if I hadn't seen her."
Natasha and Steve shared a glance. She asked, "Do you think Tony remembers that he BUILT her?"
Steve shrugged and said, "Doesn't matter. She's as real as Vision now."
Natasha frowned and said, "So he'll be no help at all."
Steve nodded and said, "We knew it was a long shot. It'll take something big to make Tony change his mind."
Scott frowned and said, "Bigger than saving trillions of dusted people across the universe?"
Steve nodded and said, "Tony has Pepper, Happy, and Rhodey. And now he has Morgan. Those trillions are just numbers. He'd need to miss someone personally to get involved. And after all this time, I'm not sure who that would be."
Scott asked, "So what are we gonna do? What, are we gonna give up?"
Steve answered,:"No, but we need to do it right. We'll need a really big brain."
Natasha nodded and leaned back in her seat as they drove to their next possibility.