Honestly, I think at this point, RPG elements are so ubiquitous throughout the gaming industry that the term technically no longer works as a genre on its own. It's impossible to get a unified agreement on what an RPG is and it's almost as impossible to explain your definition and give solid reasons.

For me these days it's just a feeling, I can immediately tell if I consider something an RPG or not, but I have no actual facts to base this feeling on.

As an example, I wouldn't consider Breath of the Wild an RPG. Why? Is it just because it lacks levels? Horizon: Zero Dawn has levels and stats and skills, but I don't consider that an RPG either.

Is it the gameplay style then? No, because I consider Deus Ex an RPG, and that plays like a first person shooter. Same with things like Mass Effect, they play like third person shooters but they're still RPGs.

The focus on story? Nah, there are a lot of dungeon crawling RPGs out there that have little to no focus on story, see games like Etrian Odyssey.

tldr: I can't explain it, I just feel it