My wife rides a trike due to balance problems.
To take it to our favorite bike path I need to put it in our SUV. I take off the seat and front wheel but the height from the bottom of the fork to the top highest point on the handlebars is just about 2" too much to fit through the back hatch.
I was wondering if there was such a thing as a quick release for the handlebars so I could tilt them down.
I could just loosen the locking bolt each time but thought maybe someone here might have a better idea.

I've never heard of such a thing...
well actually, there is, but they're stems designed for folding bikes with flat bars. They also happen to be 100% custom made for that folding bike, so they're not exactly interchangeable with bikes using off the shelf parts. example: https://www.thorusa.com/dahon/accessories/handlebar.htm

that doesn't mean you can't try it, if you know someone who is good at making things.

One of the adjustable stems on the market might work. I'm not sure how well they'd hold up to such frequent "readjustment", however.

Quick release stems are featured on some of the higher-end city/touring bikes here in the Netherlands. There is a little lever built into the stem that you can flip to rotate the stem/bars up or down. The only bikes I've noticed to have them are Gazelle, so I'm not sure if you could buy them separately - here is a link with a diagram:

link

Good luck in your search!

To pack in suitcases Bike friday split the bars in half , made a sleeve with a screw in it to press
fit in the halves of the bar the cove cut in each half of the bar aligns the parts on either side.

then it clamps in the stem .. works as a whole

need a stem as above then the allen wrench is not needed as for common parts ..

But in common parts , a quill to threadless adapter
would allow a threadless stem to skip off the top.
with a loosening of those 2 bolts that clamp the stem on.