Warning: This article contains some light spoilers for Alien: Romulus. Alien: Romulus starts with something of a goofy premise. For 20 years after the events of the original Alien, apparently, the xenomorph-obsessed Weyland-Yutani Corporation has been searching for the Nostromo and the monster its crew brought aboard.
When they finally find it, they discover the original alien that Ellen Ripley blew out an airlock at the end of that movie. Somehow, the creature survives, allowing the scientists to capture it and study it--with predictably lethal results. Alien: Romulus has to jump through a lot of hoops to create a situation in which some of the most frightening creatures ever committed to film can do their thing and scare new audiences.
It's a little peek at what kind of mess the Alien franchise's overarching story has become. The knots Romulus twists itself in so it can stay true to the story of Alien, Aliens, Prometheus, and Alien: Covenant are a pretty good argument for why it's time for the Alien franchise to drop all its past stories and start fresh. See, the setup of Alien: Romulus, where scientists find a creature that was ostensibly killed already and use it as the premise for a whole new movie, is the result of choices made by James Cameron.
They've been compounded over the years by the folks in charge of the Alien franchise, with bad choice after bad choice, and all those decisions actively hamstring the stories that the franchise can tell. Cameron famously pitched.