Ive purchased a bunch of small things that have already been mentioned.  The one thing I keep coming back to is the Mixed 5D saddle.  Great shape and padding, while only 120g.  I put one one all my bikes.  It survived a pretty abusive XC season as well.  Sure beats the hell out of a similar S-Works Power at 10% the cost.

https://www.aliexpress.us/item/3256803325810840.html?gatewayAdapt=glo2usa4itemAdapt

I just built up my s3 over the winter.  It's my first mtb so I don't have much to compare it to.  I was just looking for a budget bike I could race in some local xc events.  Tried keeping it somewhat light for a few races, but budget limited me on some things.

Specs:
Fork: Sid ultimate 120
Rear shock: Dps performance 165x45
Crank:. Stages LR XTR 36t
Shift: XTR shift/xt rear derailleur
Cassette: slx 10-45
Brakes: xt 8000
Bars: race face next 700mm
Wheels: hunt race xc wide
Tire:. Specialized ground control/FasTrack 29x2.35
Pedal: xtr

Right now I'm at right around 25lbs.  I'm thinking of swapping to some iKon/rekon 2.20, so hopefully that will lighten things up.  Have a transfer sl dropper on the way, but honestly not sure I'll need it.