My (small frame admittedly) BFeMAX was 12.8kg plus pedals, nothing overly expensive or bought specifically for weight-loss but the main spec is below. I still had 2.4″ tyres, a dropper and 4-pot brakes on it, with a pretty budget groupset:
Hunt XC Race wheelset with 2.4″ Bontrager XR4’s (these combined were the biggest difference)
Answer ProTaper Carbon Handlebars (were cheap on Chainreaction, 740mm)
Fox 34 Performance Elite at 140mm (I think these are pretty light even compared to the Rockshox more XC forks)
Sram NX 11-speed with a Hope BB
Sram Guide RE brakes (4-pot E-bike brakes!)
Oneup V2 Dropper & Burgtec Cloud saddle (metal rails)
None of it was bought specifically to be light except the wheels, everything I just picked up in sales with half an eye on weight if there was a straight choice between two parts.