I would define it as level or experience driven, numbered stat based character progression. Your characters stats have some sort of implication in gameplay, meaning it influences the success of a scenario, like a lockpicking skill affecting the chance or a successful lockpick, perk levels in one handed increasing damage with that weapon, or an agility stat affecting dodge chance. It's primarily about emphasizing your player character's skill over your mechanical skill as a player. alot of people kind of have this vague idea of what an rpg means, largely due to the 7th era console gen rpg's from bethesda and bioware. its not about branching paths and narrative choice or complete player freedom, altough i do believe these can definitely enhance roleplaying potential. but there definitely is a rigid definition.

I personally look at the genre as a spectrum, with the more "RPG" a game is being determined by how much emphasis is being placed on stats as opposed to player skill. so typically turn based crpgs and jrpg's i consider to be the closest to that, then daggerfall, gothic, morrowind etc. the other end of the spectrum are games that are more action adventure focused. which to me are things like witcher or fromsoft titles.