Here are the games from my collection that see the most repeat solo play.

ROVE

Navigating the chain of spatial puzzles is just thinky enough to not outlast the games short length.

I play all mission expansions mixed together, sometimes crawler, sometimes reconfigured. A normal game of completing seven missions takes around 10-15 minutes once you know how to play. The longer game of play until you lose can last a fair bit longer.

SpaceShipped

You are trying to outmaneuver an automa opponent to be the first to obtain two rare resources in a fluctuation market.

I like the Infinite variant you can find on bgg. Games tend to run half an hour for me.

A Feast for Odin

You alternate taking turns in worker placement in an elegant solo mode. Trying to maximize the polyonimo space you can cover with minimal actions is always fresh and fun. Runs near two hours for when I want a longer session, or a game over the course of a week.

The base game is good. The recent reprint comes with two great expansions. Norwegians completely reshapes the game into something even better if you liked the base game and want to give it more life.

Great Western Trail(s)

Build up a new each game loop of action spaces to try and maximize VP by selling cows, moving trains, and building more actions. I tend take 2 hours for a solo play.

I own both the first game and Argentina. For solo I slightly prefer Argentina, but they are tied for my favorite game on the shelf. The series is great enough that I have New Zealand preordered.