Go to the cinema
Cinema is one of the easiest plans to keep when nobody else is free. Choose the film and the time you actually want, buy a seat and go.
If you would prefer company, Costar can add the possibility of meeting another compatible adult who independently chose the same screening.
Use museums and galleries on your own terms
A solo visit lets you move at your own pace and leave when you have had enough. You do not need to negotiate which rooms matter or how long to stay.
If you want a more social version, talks, late openings and guided events create more natural interaction than simply hoping to meet someone in a gallery.
Choose structured activities
Classes, sport and volunteering work well because the activity creates a role for everyone. That reduces the pressure to make conversation out of nothing.
The same principle explains why a shared screening can be a useful first meeting. There is already something to do.
Stop treating solo plans as second best
The goal is not to fill every evening with strangers. It is to make your own plans less dependent on other people's availability.
Some nights you will go alone. Some will include old friends. Some will introduce somebody new. A healthy city life can contain all three.