Yes the highest substantive officer rank in the RAF VR(T) is Flying Officer. Some are granted paid acting rank above that depending on role. In certain circumstances you can get acting (unpaid) Flt Lt, usually time served is the criteria for this.
Strangely as an acting (paid) Sqn Ldr when I retired I was allowed to retain the rank. Don't quite know what that means! When you retire it is over, forget it and get on with life.
ACW