Solo: A Star Wars Story is centered around Han Solo's backstory. It includes characters like Qi'ra, Lando Calrissian, and others relevant to Han's journey. Darth Maul is a Sith Lord with his own story that doesn't intersect with Han Solo's early days as depicted in Solo. His story mainly ties into the events of the prequel trilogy and the Clone Wars era, not the events in Solo.
Yes. He was in it. Darth Maul's appearance in Solo: A Star Wars Story is significant. It helps to expand the story's universe and tie in different elements of the overall Star Wars saga. It also gives more depth to the criminal underworld that Han Solo was getting involved in. Maul's role in the movie was a reminder of the complex power dynamics and hidden forces at work within the Star Wars galaxy.
Maybe some of the Jedi who cross paths with Darth Maul, like Qui - Gon Jinn. Their interactions are important in the Star Wars universe. Also, there could be other Sith or dark side characters who are part of Maul's story, perhaps his own apprentices if he has any at some point in the story.
Darth Sidious is an important character. He is Darth Maul's master and plays a crucial role in guiding Maul's actions and training. Another one could be some of the Jedi that Maul encounters during his missions. They are his opponents and their interactions are significant.
He might have some underworld contacts as allies. People who are also outcasts in the galaxy and see value in aligning with a powerful Sith like Darth Maul.