That is also not what most of us would consider fixed.
If I have to set up the arrival runway during the planning stage that is not realistic for flights that exceed the normal TAF and METAR cycles.
You plan based on available information, but work with what nature gives you. Up to and including an alternate airport.
I for one always plan in LNM or Navigraph and then only load the plan airport to airport in MSFS. No runway selection on the arrival at all.