The right terminal command is
/Applications/texstudio.app/Contents/MacOS/texstudio --start-always, but you will need to keep the terminal open.
You can create an application with Automator (see here and here) to start new instances every time:
- open Automator and create a new Application
- to add
Run Shell Script drag and drop it from the list; might need these settings
Shell: /bin/bash and
Pass input: as arguments
- insert the code below; if necessary adjust the path to your TeXstudio executable
nohup /Applications/texstudio.app/Contents/MacOS/texstudio --start-always > /dev/null 2>&1 &
- save the script as an application (!)
You can now place this into your application folder.
If you have a look at the jupyter-version, you might think it could also work when opening files. However, I have not yet tried to re-associate files with this script in order to open a new instance for every file (since you can open other files as usual, e.g. drag and drop). This would also need some logic to differentiate between plain calls and calls with file-paths passed, I guess.