The basics – intelligent, thoughtful, not racist, not sexist etc, not mean, not controlling, not prone to violence, respectful of others, kind to waiters, children and the elderly – go without saying.
The big one for me is that he needs to understand that he's responsible for his own happiness. I had a long early relationship with someone who was depressive and who seemed to think it was my job to make him happy.
Otherwise...
Relatively clean
Relatively tidy around the house
Able to laugh at himself and life and me without making me feel humiliated
Moderate drinker, no recreational drugs, no smoking, no vaping
Relatively competent: able to cook, clean, drive and do some basic DIY
Not clingy
Calm in an emergency
Financially independent/ solvent
Able to get on with pet projects without requiring me to help
Appreciative and respectful of difference. I'm a great reader, he'd rather be out on his bike.
I have a partner who fits most of those criteria. We still have a way to go on the projects situation. He is building a studio in the garden which he plans to use as a workroom. He expects that I will be happy to stand around for hours while he decides what needs hammering in next or waiting for the moment when he needs me to hold something in position. We are working on this.
I'm not perfect either.