I work on only one project and each time I run the editor I have to select that sole project. Is there a way to have the editor auto open the last used project?
If you start godot from the command line, you can provide the path to a project:
godot --path "<PathToProject>"
Alternatively you could instruct your file manager to open the project.godot-file with Godot and then start your project by clicking on that file.
project.godot
Details may vary depending on your operating system.
On Godot 4.3, I had to run
godot --path "/path/to/project" --editor
Otherwise, it would just run the project rather than open it.