A task can depend on multiple previous or next tasks within the same project.
NOTE:
It is not supported if a task exists in multiple projects.
It is not applicable for subtasks because subtasks are already connected to their parent/main task.
How to add dependencies to tasks:
1 - Open the task and its properties window.
2 - Click on the "+" button in the Dependency section.
3 - You can select multiple Previous Task(s) and/or Next Task(s) to link the current task to them, meaning you must always complete the linked task(s) before moving onto the next.
How to remove dependencies between tasks:
1 - Click on a task with the “Dependency” sign to access its properties window.
2 - Click on the existing dependency.
3 - Under the list of Previous Task or Next Task, hover the mouse over the desired task and click the "x" button.


