I remember that Ursula and Divine connection, it’s hard for me to judge if at each case someone really wanted to make them (the characters) gay coded or just wanted to give them specific traits, much different from the protagonists, the good characters etc... I wonder to what extent it was any real coding or just stereotypes.

That's is a moot point.

The whole thing with coding is that writers use it as a way to imply a character is from x demographic without having to explicitly cite it in the text.

Stereotypes are an easy way to this because they're recognizable by most people.

Because when I was reading various threads about gay-coded characters I had this thought: “ok, maybe some LGBs act like that but not all” and it’s sexist to claim that because a character has specific mannerism, they must be gay. Maybe that’s also due to different reception of overlooking of that theme (if it really exists) in my country. For example I personally never saw Scar as gay and I don’t know a person who did.

A character doesn't need to be of x demographic for coding to be a thing. That would be antithetic to coding itself.