Characters off the top of my head -
DL:
Fantasyland:
Gaston
Evil Queen
Peter Pan, Wendy, Captain Hook
Alice & Mad Hatter
plus fairly often:
Mary Poppins & Bert
Moana
Merida
various roaming princesses (often Belle) and Anna & Elsa
and recently:
Pinocchio & Geppetto
Frontierland:
Mirabel and Miguel.
You might spot Tiana on the Mark Twain.
Critter Country:
Various Pooh characters.
Star Wars Land:
Mando & Grogu should still be out. Possibly Boba Fett and Fennic Shand but not sure as I don't visit that land. Plus regulars like Rey, Chewie, Kylo Ren, Stormtroopers and First Order.
Toontown:
Fab Five and new character Pete
DCA:
Pixar Pier features Pixar characters regularly - generally Woody, Jessie, Buzz, Bo-Peep, Joy and Sadness. Mr. Incredible, Mrs. Incredible and Frozone are also around occasionally.. Seasonal events also bring out Carl, Russell and Dug.
Judy Hopps & Nick Wilde are often around the corner from the Little Mermaid attraction on the way to Grizzly Peak.
Cars Land has Lightning McQueen and Tow Mater regularly.
Avengers Campus averages at least a dozen characters out daily and sometimes nearly 20. I can run through the list if needed.
Fab Five are all over both parks but especially Main Street at DL (Cruella hangs out there, too) and Buena Vista Street at DCA.
If you're looking for anyone else specifically, just ask.
(These are just the main regulars. Others pop in and out at times, too.)