It used to be a much more difficult undertaking to figure out which Marvel characters fell under which studio umbrellas. Marvel previously sold off many of its characters to other studios, including Paramount, Sony, 20th Century Fox, Universal, and more, but since Disney bought Marvel the House of Mouse has slowly but surely put the toys back into the toy box. Now the only outlier is Sony's wealth of Spider-Man characters, but there's still some confusion as to what they own and what is still under Marvel, so The Geek Twins have put together this fantastic graphic and updated it to reflect the newest additions to the universe, which should solve most of the big questions.
The graphic is separated into four bubbles, though some overlap. The largest bubble is Marvel's of course, as over time they've made deals with Universal for the Hulk characters (as you can see in the overlap) and they recently got back all their X-Men and Fantastic Four characters thanks to that landscape changing deal Disney made to buy 20th Century Fox and all their assets from 21st Century Fox.
There are two bubbles that exist outside of Marvel's, and those are Netflix (green) and Sony Pictures (blue). The Netflix one is only there for the moment, as eventually the two years on that contract that forbids Marvel from using those characters will run out and then Marvel can start using them again.
The second one is Sony though, and that doesn't appear to be going anywhere. In that graphic are characters like Spider-Man, Carnage, Black Cat, Venom, Spider-Man (Miles Morales), Green Goblin, Doctor Octopus, and Kingpin, despite also sharing rights with Netflix for the character.
Unless Sony and Marvel can work out a new deal to share those characters like they did with Spider-Man: Far From Home and Avengers: Endgame, it seems those characters will be staying put in the Sony side of things and not the MCU, but who knows, maybe things will work out. In any case, you can check out the awesome new graphic above.