Click the 📖 Projects icon and select the project that you want to open. This will open the project URL and switch to the view mode or preset that you chose while creating the project. In addition, you'll see the bookmarks, todos, and notes linked to the project (if any).
While a project is activated, you'll see it on the top of the projects list with the label Active.
Hover over the active project and click the ❌ Deactivate Project icon.
If you specified a local folder and/or a code editor while creating or editing a project, you can open it in your file explorer or preferred editor by hovering over the project name and clicking the respective icon.