There are 87 different single-player tabletop RPGs in the Solo but not Alone. That's an incredible number, and strong evidence that roleplaying by yourself is an increasingly common thing to do.
Can you play a tabletop RPG by yourself? Yes, in a way, you can. There are some articles on Geek Native that might act as a starting point. There’s How to play a tabletop RPG by yourself and Fiona L.F.…
Based on older versions of D&D, especially D&D 3 and 3.5, the D20 Go rules engine now allows combat to be completed with one dice roll and then narrated by the group.
The Shrike generates one-shot GM-less RPGs about skyship voyages. At least, sometimes. If you can keep the machine chugging for the next five or ten minutes, you'll have the Prologue, and Chapters One, Two, Three, and Four.
The Blighted Well takes the idea of Fighting Fantasy style gamebook, adds isometric dungeons, more rules and creates a more fully-fledged solo RPG experience.
This solo-RPG isn't just a murder mystery, you'll have to work to stay alive as everyone seems to have secrets. The chances are high that you'll die.
In response to the Covid-19 crisis, Ulisses Spiele has made that English language version of The Dark Eye a Pay What You Want game at DriveThruRPG.
The future of D&D, the possible future of D&D Beyond and enough RPG Zines from Kickstarter to break any set of shelves.
Many RPGs can be adjusted to fit a single player, and as a result, there are no limits to the stories that can be played alone.
The Solo Adventurer's Toolbox is a Fantasy Grounds MOD that adds in random quests, random encounters, the ability to create dungeons randomly, wilderness exploration and town settlements and NPCs. The toolkit creates random NPCs including merchants with shops, and they say infinite monster encounters.