The official policy is here: https://www.qatarairways.com/en/help...gage-allowance and that should be your baseline in case QR wants to go by the book.
Off course YMMV based on the day, equipment, load factor and of course on what kind of day the ground agents are having.
As a data point, my carry-on has only been weighed 1-2 times in outstations (never in DOH) and even when i have travelled with a wheeled cabin carry-on and a back pack i had no issues (I'm QR Gold/Plat).