"...Preferably a portable tripod to fit in backpack…"
Photojournal you're wanting to hang a 4 lb lens on this? Really?
Sturdy isn't light... nor is it cheap... you're looking at maybe carbon fiber...
However please tell us what genre you work in... That is pivotal to the mix here.
There is a vast difference between shooting Polo and Fashion Editorials.
I shoot fashion and beauty editorials on location with a fluid head on a Carbon Fiber Sirui ET 2204 US albeit that is certainly not going to work for your 4 lb plus beast...
https://www.bhphotovideo.com/c/product/1456057-REG/sirui_suet2204l_et_2204_tripods_legs.htmlIt's only 3 lbs albeit the fluid head is another couple of lbs on top of that...
You can't have long glass and light weight...
So funny how folks never seem to learn until the brutal truth of reality kicks in...
btw, I make big bucks as a photo assistant for commercial shooters in my market who use massive tripods on location. It's exhausting work, long hours (up to 14 hour days) but I'm smiling on the way to the bank.
Bottom Line? Perhaps you may benefit from the services of an assistant?
Yes US Marines can endure a 40lb plus loading and move quickly over rough terrain...
But then again they are highly trained endurance athletes.
Maybe consider renting one first?
https://www.lensrentals.com/rent/video/tripodsIf you're only shooting a couple of location events per year this is an excellent solution.
btw, the naive pay twice... once to figure out that they seriously need to pony up considerably more for the appropriate tool for the job... Just saying...
Wishing you all the best on your journey Photojournal