Pinterest not the perfect place to find good ideas that are practical. Yes this is a bad idea and in many cases just not workable and IMO if the vent needs a bend this is the wrong place for your range . At the best of times 900CFM is not enough for a gas range and when you add a 90 degree bend you will need to up those CFM even more than if it was staraight up. Post some pics here of the floor plan to scale nad see what ideas come . Post in a comment DO NOT start another post. FYI just becuse you see it in a picture does not make it a good idea.

There is a limit on how you can cut through Joists. I would suggest discussing with your installer. Also, you will need a make up air system for cfms that high. I would have this conversation with the person who is doing the work since we can't see what the structure of your home is and what may be possible.

Good luck

90 degree bends equal five feet of duct length each so they take 10 feet off the allowable length.

I think it would be better if it were able to bend and go up through a stud space in the wall of the bedroom. This may be possible if you can transition to an oval 4 x 14 = 7.8" round or 4 x 15 = 8" if those are adequate duct sizes. When you say "through joist" do you mean "in a joist space" ?