Where does this little metal bracket in my gas oven belong?

Those offset L-shaped stamped brackets with bent tabs and a pair of screw holes are usally burner or electrode mounting brackets in a gas oven, not door glass hardware. Door glass panels sit in frames and clips made of heavier gauge steel or wire, they don't use tabs like that. The tabs are there to grip and align whatever it holds before you tighten the screws, wich is why it looks weird and half-formed when you find it sitting loose on the insulation.

Yeah that matches what I pulled out of my old range a few years back. Same stamped bracket, same bent tabs, and it turned out it clamped the burner tube down at the back. Mine had worked loose just enough that the burner sat crooked, and I got exactly the slow heating and lopsided baking you're describing. I lined the tube back into the tabs, snug the screws down, and the uneven heating went away basicly overnight. So yours might not even be missing a spot, just a loose one. If you look under the burner tube near where it sits, you should see empty screw holes close by.

Been fixing ranges since the days when the manual actually came printed in the box, and that bracket is a common thing to find rattling around in older ovens. Before you button it back up, light the burner and watch the flame spread across the bottom. If it's lazy or hugging one side, the tube still isn't seated right. Old trick my father used: sprinkle a spoonful of flour on a cold cookie sheet and bake it, you can read the heat pattern right off the browning. Also grab those screws snug but not gorilla tight, the stamped metal strips easy.

I'm not buying the story that the bracket falling off is what made your oven cook lopsided. On the ranges I've opened up, the burner tube screws into its orifice fitting at the front and that's what actually holds it in line. A loose bracket rattling around on the insulation can't shift the tube by itself, it just stopped doing its job. So if your flame is hugging one side, I'd look at the igniter or the tube's mounting at the front end, not assume the bracket was the cause. coud be a previous owner left it out after a repair and the uneven baking is a seperate issue entirely.

While you're in there, poke the little holes along the burner tube with a pin or thin wire. I chased the same lopsided baking on my range for months and reseating the bracket didn't fully fix it. Turned out the ports were half plugged with grease and crumbs, so the flame spread was weak on one side even with everything bolted up right. Vacuum out the crumbs first, then clear each hole. And if you end up unscrewing the tube from its fitting, mix some dish soap and water and brush it on the joint after the gas is back on. Bubbles mean it's not seated. I also snap a phone pic of the whole assembly before touching anything, saves guessing later.