A number of people have made and published their own settings using the GURPS system. Here are some of them.
- Icelanders Worlds - A discord channel on the Unofficial GUIRPS Discord server.
- Psi-Wars is a space opera setting inspired by Star Wars.
- Nen Psi Powers - Adapting Hunter X Hunter
A lot of people have already played other game systems or have stories they would like to play based on settings from novels, movies, or even TV.
I do not recommend converting a game system. It will be a lot of work and will not perfectly convert. However converting a setting is often more satisfying, even if that setting is in another game system.
Check out the published settings for official adaptations of many novels. Most were in GURPS Third Edition but converting to Fourth Edition is not that much work.
Dark Souls YouTube rundown.