From here.
In Xcode, when you press “Shift + Command + O” to use the “Open Quickly” feature to open a file, by default the file will be opened in the existing tab instead of a new tab. However I want to change this behavior to open the file in a new tab. This can be done by the following configuration:
Press “Command + ,” to open “Settings”. Go to the “Navigation” tab.
Update the “Optional Navigation” by setting its value as “Uses Tab”.
Done.
Now when you press “Shift + Command + O” to use the “Open Quickly” feature to open a file, after searching and selecting the file, press “Option + Enter” to open it. Now the file will be opened in a new tab.