n ProjeQtOr, it seems that you only have the choice of Finish to Start.
Yes.
Start to Start (SS) - This schedules the activity to start at the same date as it's linked activity
Add milestone as prior of both tasks.
Start to Finish (SF)
Define a Finish to Start in the other way round.
Finish to Start (FS)
This is the only existing in ProjeQtOr
Finish to Finish (FF)
Cannot reproduce in ProjeQtOr : this one will need a reverse planning and may introduce overloading for resources, what is not possible in ProjeQtOr.
Another concept is how Planning works in ProjeQtor
ProjeQtOr is "work driven" (called Effort driven in MS-Project)
We do not use the work effor for scheduling. What is the best way to accomplish in ProjeQtOr?
Use fix duration planning mode. You can set is as default planning mode (in Activity type)
Should we set all activities to fixed duration?
Yes, if you do not use effort driven planning.
is there a way in the planning mode to expand group levels one at a time
No, but it is subject of Ticket #1744.