This question makes me think of The Tragedy of GJ237b (https://medium.com/@balehman/the-tragedy-of-gj237b-928cfeae460b) which positions itself as an "A role-playing game for no players". I think the meta-narrative is deliberately unreliable, because in essence the game is you pretending that someone has a game going in a room you can't visit, and once you do you process the loss of people you'll never meet. So you're the player just by setting it up.
I wondered at the time if it counted as a game, as my mindset would argue a game needs 'play' (without trying to define that) as opposed to other group rituals, and players to create that play. But there was a whole discussion around it that asked about games that we no longer had complete rules for so couldn't play, like the Game of Ur. Are they still games? It was a good thought exercise at least.
I'm not sure what makes a solo LARP explicitly a game and not a ritual, although it could be both at the same time. But for myself, I think that a game requires (1) instructions, however sparse, to separate it from unguided daydreaming or activities, and (2) play, which I'm going to fail on defining because it doesn't have to be about recreation or fun but I think of as a guided activity that performs some sort of recreation.
Not sure if that helps at all XD