RPG usually suggests stats, some form of inventory management, and some form of character decision making as you level (e.g. allocating stats, or picking the right equipment and gear, etc).
In the 90s and 00s, that was the main criteria, because most games didnt have RPG elements (e.g. no levelups, no party management, no inventory management, etc). Symphony of the night for example, was initially described as having rpg elements because of the stats and gear, but in mixing rpg stats and inventory with metroid, we got metroidvania as a genre.
Nowadays it feels like some people use RPG for mechanics (stat management, inventrory, etc), while others use it to mean narrative agency (e.g. making decisions that impact the story and quests).
But its all muddy now because of ARPG as a concept, and how few "pure" genre games exist anymore. Everything borrows mechanics from everything, so its now just a marketing term.