So you enter the STAR and Approach shortly before landing at the time ATC give you the instructions and this is working for you without changing other waypoints? I’ll try this will be helping.
Because I use a offline ATC tool (Pilot2ATC) I can define if ATC can assign SID/STAR/Approaches and therefore I can also create a fixed route which is not changed anymore.
The behavior where the aircraft is returning to origin I’m was facing too in before but the heading mode was my friend here too 