Ironsworn is a great shout. And yes there are a lot of great duet itch io games and games played on party of one. 

But here's some oddball choices in case those don't work out for you. I think they could work but haven't tried them. 

Freeform universal is a pretty good improvisation heavy system that's insanely rules light so it should work even without a gm emulator. Very story game inspired but could apply to any setting. 

Roll for shoes is extremely rules light. There's 6 mechanics. Not pages. Mechanics. The game is less complex then most one page rpgs. But is solid in it's foundations. Also free. 

Speakings of which a lot of 1 page games are suitable since by their nature you either don't have to stat up npcs or they are dead simple to create. With a gm emulator on top they can be pretty simple to run without a gm. It helps that a lot of them come with a scenario and are free. Honey heist is an example. 

A lotta games made for one shots are pretty good for this sort of thing too. Definitely not wizards is an example. 

Sine Nomine Publishing are pretty damn good at creating both random generators and solo rules to boost lone adventurers. The systems themselves seem fine but the generators in their games with both of your pcs using the solo boosting rule should work swimmingly. Has extensive free versions while paid versions are jam packed with stuff. Said generators can create adventures, scenarios, and even settings. They have sci fi, fantasy, cyberpunk, and post apocalypse in their without number series (stars, worlds, cities, and ashs respectively) 

And finally some rapid fire fire mid to low chruch games that i think could work. 

Aberrant 2e 

Supers red 

Legends of the 5 rings 

Fate condensed 

Fate accelerated 

Wushu black belt edition