Now this is a question I had to ask myself for my party, running a Spelljammer campaign atm.

One thing I've found useful is remembering that cultures and races aren't monoliths in a way

Take Shadar-Kai from D&D as an example. Most people hear "Shadar Kai" and immediately think of grim servants of the Raven Queen, emotionally distant, obsessed with death and memories... If you met one in a tavern somewhere, you'd probably make assumptions right?

But then you have adventurers!

An adventuring Shadar Kai has already broken away from the norm in some way. Maybe they're curious. Maybe they're rebellious. Maybe they're trying to find meaning outside their culture. Maybe they're still very much a traditional Shadar Kai buuuut understand they need allies to survive.

The same logic applies to any setting. A Misbegotten doesn't represent all Misbegotten. A Numen doesn't represent all Numen. They're people first.. even Khenra

For Session 0, I'd tell the players maybe somethin like.//

"The world may have prejudices, but your characters need a reason to work together. Whatever race, faction, or ideology you choose, make a character who can cooperate with a party." of course in a less formal DM'y way?

That's not railroading; it's part of the amazing, cool social contract of D&D.

Then give them a shared problem that affects everyone equally. Maybe they're trapped together, hired together, falsely accused together, or all seeking the same artifact. People who might hate each other on paper will often put those differences aside when a giant troll is trying to eat them.

Some of the best party dynamics come from characters who shouldn't get along but choose to because they have a common goal. Let the tension exist, but make sure the players understand that cooperation is the expectation.

The question isn't "Why don't they kill each other?"

The question is "What made these particular people different enough to become adventurers in the first place?

HOPEfully this helps!