The King Air 350i does not have a mixture control, because it has two turboprop engines.
Turboprops use a different type of fuel control called “condition levers” that have usually three positions: Fuel Cut-off, Low Idle and High Idle; in that order working from down to top position.
Fuel Cut-Off is used when shutting down the engines, as its name says.
Low Idle modifies the maximum and minimum N1 usable (62-104%).
High Idle modifies usable N1 too (70-104%).
This lever has free movement and an off-center “notch” for the low idle position.
Apparently the last update has made it so that you can only select high idle, low idle or cut-off and nothing in between, much like in the real plane but kind of synthetic.
You don’t need to adjust the mixture on a turboprop, they are turbines.
I hope this clears some of the confusion, there’s a lot of information online about the differences on carbureted, fuel injected, turbo-charged, turboprops, turbines and turbofans.
I recommend, if you’re interested in aviation, you take a look at this book which is one of the basic books student pilots use. It’ll be of great use on the sim too, especially if someday it reaches a higher level of systems simulation.
I’m linking to Ch.7 which is Aircraft Systems. The book is free on the FAA website, along with some others on their free library.
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/09_phak_ch7.pdf
Have fun!
P.D. Here’s the link for the book
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/