I'm planning on two solo campaigns, one with EDGE Studio (originally Fantasy Flight Games) Star Wars RPG. A mix of both Edge of the Empire, Age of Rebellion, and Force and Destiny further down the road. But I plan on running it during the Old Republic era. I quite enjoy playing the SWRPG/Genesys system. I know the narrative dice is hard to get behind for some people but I prefer it. It feels a bit more transparent what you'll get, plus it's fun to roll a lot of dice so there's that tactile aspect to it too π
The second campaign is with Ironsworn: Starforged. I actually want to use this solo game as a basis for my web serial that I want to write in the near future. The system is built with solo play in mind, but it can be played co-op or guided by a GM. IIRC, the original basis of the system was PbtA, heavily modified. Ironsworn was what introduced me to the concept of playing a TTRPG solo! Which was awesome, considering my previous experiences playing a TTRPG with a group keep falling apart for one reason or another...
I also want to try City Without Numbers, the cyberpunk variant of World Without Numbers and Stars Without Numbers. I backed it on Kickstarter and sorta waiting for a slightly more complete version before I dive in. Again, it's something I plan on running solo as well...
I am considering a play-by-post game, likely with the Ironsworn: Starforged system. Largely because of the nature of PbtA games, which tends to give and encourage more agency to players. Plus the support for running it co-op means ideally, no one is relied on as the GM, constantly having to respond to a player's inquiry or action before anyone else can move forward.