I would say the best beginner heroes are soldier, reaper, reinhardt, lucio, and mercy personally. All of these teach valuable fundimentals of the game without being excessively mechanically challenging.
Soldier shouldn't be too hard if youre used to playing cod or something similar. Pretty generic damage hero for the most part.
Mei isn't too hard but using ice walls properly takes some practice. You want to use them to split up a team so you can fight them 6v1 or 6v2. This can be a little bit tricky when you're just learning her, but there are a lot of guides online describing how to properly utilize her walls on the internet so I would look at some of those if you're interested.
Lucio is a good beginner hero for sure, and he's also an extremely helpful one. Imo everyone should have Lucio in their hero pool because he's one of the best in the game and he's not too difficult to get the hang of.
Ana is a little less friendly to beginners, but if you put in the necessary effort you can definitely be good at her. She requires a little of everything. Aim, the ability to compensate for projectiles (unscoped shots + sleep dart), positioning, and decision making. Still, if you're willing to take a challenge she's a great hero to play.
