Given that Qatar isn't an approved airline for transit AND isn't one of SQ's approved partner for transit (sq & some of their partners are approved)
So no, you can't transit with your itinerary right now
https://www.changiairport.com/en/air...h-airport.html
https://www.singaporeair.com/en_UK/s...t/?id=kataac8r
Transfers in Singapore are only allowed on flights between airlines within the SIA Group (Singapore Airlines and Scoot). In addition, SIA has interline agreements with Air France and KLM Royal Dutch Airlines, Air Niugini, Garuda Indonesia, Lufthansa, Swiss International Air Lines and Turkish Airlines which allows their customers to transit through Singapore Changi Airport from cities approved for transit flights to destinations in the SIA Group network currently operated by Singapore Airlines