It would probably depend on the school.
E.g. USYD forces you to graduate
https://sydney.edu.au/students/graduation.html
However, You can still take more units even if this is the case: E.g. say you needed to take a particular core subject to graduate, then you can always keep taking other units and hold off on taking that final required subject until you want to graduate.
Not sure why you would want to stay back, but yeh you can if you want.