You can pin folders that you frequently need to access to the Dock on macOS. When you click a folder on the Dock though, it doesn’t open in Finder. Instead, you either see the ‘fan’ view of the file in it, or you get a little window that allows you to browse the file inside the folder. If you prefer the folder just open when you click its icon on the Dock, macOS won’t let you do that. That’s not to say there isn’t a work around for it. To single-click to open folders on the Dock, you need to create an Alias for the folder and then add it to the Dock.
Folder alias to Dock
If you have the folder in question pinned to the Dock, unpin it first so that you’re not using up unnecessary space. To unpin it from the Dock, right-click the folder and from the Options sub-menu in the context menu, select Remove from Dock.
Next, open Finder and navigate to the folder that you want to open with a single click. Right-click it and select Make Alias from the context menu. The alias will be created in the same folder. You can choose to leave it there, or you can move it to a different folder to keep things organized.
Regardless of where you eventually place the Alias, you need to first add it to the Dock i.e. pin it to the Dock. You can do this by dragging and dropping it on to the Dock. Hold it over the Dock for a few seconds until it makes ‘space’ for itself and then release it to pin the Alias.
When you click the Alias, it will open the folder that its for in Finder. You need only click it once.
This functionality used to be present on older versions of macOS but has since been replaced with the newer previews. The previews aren’t a bad idea. A lot of users can benefit from a quick way of browsing files in a folder without having to go through the Finder but it doesn’t negate the need to open apps or folders with just one click.
For users that are exclusively using a touch pad with their Macs e.g., users with MacBooks, using the context menu to open folders in Finder from the Dock isn’t exactly going to be a quick or intuitive process.
As far as apps are concerned, you can launch apps by simply clicking on their Dock icon. If an app is already running, clicking on the Dock icon will maximize the app’s window or switch you over to it. It will not launch a new session or window of the app.