Singapore could potentially make an exception for these transit flights - e.g. if they put it at T3 Gates A1234 or B1234 then there are toilets and a kiosk you can access without clearing security.

Otherwise needs to be somewhere they can position the crew who are currently in Singapore to, my guess would be KL since it has the same security setup as Singapore so works well for a transit. Not sure if there is a exception for crew to access a hotel (they could go to Sama Sama outside the airport and "quarantine")