If you’re going to do it, it’s all in the details. Starting off with a 5lb frame is never going to be the best place to start from to make a lightweight XC bike (I asked a similar question about my own bike months ago, with a 4lb frameset)… But crucially as the frame is dead weight, then it’s one of the least important areas to lose weight overall.
Wheels and Tyres will make the single biggest difference to how the bike rides. Borrowed a pair of 1600g wheels shod with super light Maxxis Ikon’s when I did 24/12 solo last year. They saved almost 1kg of rotating weight compared to the wheels and tyres I was running at the time! Look at something like the Light Bikes carbon rims built into DT swiss 240 hubs or the like, with very light spokes, and you should be coming in at around 1500g but still plenty stiff. Then just pick the light, fast rubber of your choice and don’t forget to run tubeless.
Beyond that… Don’t get hung up on things like lightweight saddles and grips. If you’re spending lots of time on the bike, comfortable contact points that you know you can rely on make all the difference.
Drivetrain wise, you can save plenty of weight by going to 1x 9/10/11. But… You need to know you can get the hearing right to suit, and if you can’t get a 1x setup to go low enough for your own requirements, then it would have a detrimental effect on your performance far more than the weight saving would otherwise realise.
If you really want to compete, you’ll find a way to throw money at carbon or titanium for everything on the bike. Otherwise just make sure you’ve got some light/fast wheels and tyres, and don’t worry too much about everything else. Enjoy it for what it is, a test of your own personal abilities, not so much those of the bike.