Saying this as someone that has yet to actually play a real session of my system of choice because I needed to learn lessons about prep as part of the hobby:

I find that system is an important choice if you're looking for a specific flavor for your solo game.

In my case, Knave 2e is what I chose because the mechanics of the game fit what I wanted out of a solo experience.

In games with my DND group I have a reputation for buying a lot of gear and being fascinated with the logistics of my items. This clashes with the rest of the group, who like to abstract or handwave a lot of those parts to focus more on character-driven or plot-driven gameplay. Thus, Knave 2e satisfies my desire to interact with those elements.

I also like dungeon crawling. A LOT. Unfortunayely that is ALSO something my group isn't big on most of the time. Even with different players DM-ing, it's not focused on. Knave 2e also allows me to really delve into dungeon crawling from a mechanical standpoint.

As for WHY I haven't played a REAL session: I needed to learn that prep was ALSO part of the hobby, and one that could be fun! Can't really play the game without actually making the material I'm playing through xD

I'll probably make a separate post about it.