Grid position in UI doesn't work. If select 25 on 25 car field and skip through practice and qualify by using finish session or skip session you will always start first , its impossible to start at back of pack unless you let the whole field qualify in real time and do not set a lap time or set slowest lap time.
you could use time acceleration And yes, it is broken. Marcel Offermans wrote at discord they will have a look on that issue