long story short, i would like to temporarily use a 12 speed eagle mech with 11 speed kmc chain , sram cassette and sram shifter. will it work?

Yes*

Everything I have read trying to find out if an 11-speed mech will work with Eagle cassette (nothing) says 12 speed mech works in 11 speed cassette.

*Possibly.

Why wouldn’t it? The shifter determines the amount of throw for the cable. The mech just moves the available amount.

Yes but different rear mechs have different pull ratios although in this case I’m pretty sure that I read that it works fine .

https://bicycles.stackexchange.com/questions/44178/sram-x01-eagle-12speed-in-11speed-transmission-it-work

Cheers i’ll give it a go.

I’ve heard it works, as it’s how I can get a 50 tooth on my NX11 setup.

Let us know before I buy one 😉