Upthread,
@Pedantic mentioned Suits's account of
what is a game:
To play a game is to attempt to achieve a specific state of affairs, using only means permitted by rules, where the rules prohibit use of more efficient in favour of less efficient means, and where the rules are accepted just because they make possible such activity.
Even a freeform, mechanics-less RPG fits this account, assuming that it allocates distinct GM(esque) and player(esque) participant roles. Because the most efficient means for generating a fiction about the doings of some protagonists is
for someone to tell that story. Achieving that same state of affairs - ie creation of a fiction about the doings of some protagonists - via the distribution of participant roles, and corresponding formal or informal constraints on what, and how, each participant can add to the fiction - is adopting
less efficient means. And those means are permitted by the rules (be they formal or informal rules), And the rules are accepted
because they make the fun activity of freeform RPGing possible.