RPG

You can play D&D and similar games solo but they usually require some help and extra tools to do so. Might I point you towards the [email protected] community? They might be able to answer questions and help you get started if you want to give it a try.

I love playing solo! It's a different experience versus playing with a group though. Check out Me Myself and Die on YouTube for a good example, although keep in mind he keeps it tightly edited so you don't always see his full thought process.

I have never attempted to play D&D solo, but I have discovered other RPG’s that are designed to be. Ironsworn and Starforged are both built for the solo adventurer.

Some of the older adventures (AD&D, first and second edition) were written as single-player modules, kind of like the adventure game books of the same historical era. They're sort of like Choose Your Own Adventure books, but with RPG engines bolted onto the side controlling some of the paths taken.

Yes. You use a GM emulator like Mythic. A GM emulator is basically a bunch of random tables you use to help you answer questions you'd normally ask the GM.

There is RPG more suited to played solo than D&D.

I'm not a DnD player, but it's my understanding that you usually have a DM to guide the session and write/improvise the story that your players experience and react to. I don't know if that's possible in DnD by yourself, but you might be able to something like Gloomhaven, which had the DM and story built into the game. Then you're free to enjoy the story that it's created from a player perspective.

Obligatory "Me, Myself and Die!" mention. The season one from three years ago is still a brilliant watch. Trevor plays Savage Worlds here, but you can see how the engine that makes the solo play possible is utilized. That can give you ideas for how to use it with your system of choice.
Me, Myself and Die! Season One

Slight adjacent to the topic, I wonder if Chat AI would ever be good at this sort of thing. Chat based adventure or pbp style 🤔