A Solo sequel plot could look something like this:
A couple of years have passed, and the Falcon's starting to look pretty shabby, even compared to the end of the first film. It's not ANH bad, but it's pretty bad. Solo & Chewy have adapted well to their new life on the edge of the law, working for anyone with money - mostly Jabba the Hutt, but also others, and they keep getting into scrapes, because it's them. The life isn't easy, but they make it work, together, and they are free. Ish. Qi'ra, meanwhile, under her mysterious boss's tutelage, has become a formidable crime boss in her own right.
One day, Qi'ra runs into the duo "by chance," (totally not by chance really) and offer them a no-strings job for mediocre pay. Money's money and they're feeling a bit penniless, so they take it. Except that they've been grievously mislead - the target is actually valuable as hell, but it was hidden inside the original object (for to smuggle valuables, one must be sneaky) and that object gets bashed to bits in a hectic escape sequence. Anyway, the pair weren't the only ones looking for this thingy (let's say... a long lost Jedi/Sith holocron) - turns out a couple of lean mean bounty hunters (I'm thinking Boba Fett and D'harhan?) were also on its trail, and very quickly corner our heroes before they can offload it. Figuring its worth to be rather monumental, and none of them wanting to give it up, they decide to unite and demand a much larger sum, and split the take 4 ways. Qi'ra refuses, however, so they take off and find a new buyer in the core, and they all proceed to betray each other en route to the galactic capital - someone alerts their bounty hunter friends, someone else alerts an Imperial contact, someone alerts Enfys Nest and maybe Lando too, I don't know. None of them know the others' betrayal, though.
Qi'ra leads the pursuit, but Maul decides to take matters into his own hands and goes to head them off himself.
At some point, the gang figure out they're being chased, so they split up, taking identical-looking packages in different directions to throw off the pursuers, supposedly to reunite on Coruscant.
Qi'ra confronts Solo, who is saved in the midst of a gunfight by Nest's sudden appearance. Maul faces the two bounty hunters, killing their friends and, impressed by the pair's survivability, convinces them to turn on their former partners, and they all head to Coruscant to set up an ambush before the rendezvous. Maul gets called in by his master at this point, leaving the bounty hunters to their bloody business. A scene with Maul & Sidious might involve a minor Vader cameo, perhaps Tarkin, and/or cameo mentions of rebellions and whatnot, maybe a clarification of Maul's role in the Imperial order to the audience.
An Imperial fleet, hastily arranged, blocks the path to Coruscant, but Chewy gets sneaky and passes it by while it's still forming up, while Solo and Nest find themselves stuck figuring out a way past it - they eventually settle on piggybacking the Falcon on the back of a very large freighter, right in its sensor blind spot. It'll take a lot longer than they'd like, but it works.
Chewy gets planetside and confronts the bounty hunters, and they get into this big fight, which is turned on its head as that Imperial contact, never a reliable chap, leads a Stormtrooper division to the site and aims bring them all down.
D'harhan is wounded most horribly in the ensuing firefight, which sees the Imperial commander killed (or at least wounded), and both Fett and Chewy also suffer some minor injuries, but all three make it to one of their ships and escape, heading to the rendezvous site. At about this time, Maul re-emerges from his meeting and sets off in hot pursuit, while Solo and Nest are finally down to the planet's surface. The two groups swap the real item for a fake one, and the exchange goes off without a hitch, Maul arriving just a little too late, killing the mystery buyer and taking the fake object instead.
Qi'ra, who knows Solo well enough to figure the ruse out, boards his ship while the exchange weon and at gunpoint orders him to hand over the real deal when they get back. After a tense exchange, Chewy blows her legs off with his bowcaster and they lay her in a flower bed near the landing site to die in peace. Maul recovers her and she gets his hand-me-down spider legs and plots revenge. D'harhan recovers as well, and gets his badass head-mounted cannon.
Cue the threequel.