Yes it’s possible, but depending on your Xcode version you may need to adjust the default behavior in Xcode’s preferences.
Use ⌘ command+⇧ shift+O to open the “Open Quicky” input box, and then:
- Use ⌥ option+Enter to open the file in the right editor.
- Use ⌥ option+Shift+Enter to select where you want to open the file using the arrow keys.
On Xcode 12, the default action of ⌥ option+Enter is to open the file in a new “Tab” (which are new in this release, and different from a “Window Tab”). This is still configurable in the preferences.
On Xcode 11, you can split the editor as much as you want. This means ⌥ option+Enter by default will open the file in the editor next to where your cursor currently is.
This behavior is configurable in Xcode’s Preferences, under Navigation:
To have ⌥ option+Enter open the selected file in the editor on the right of the Xcode window, select “Optional Navigation: Uses Second Editor”.