Diagnosis
That haze is polymerized grease—fat that's baked onto the glass into a hard, clear coating. Standard glass cleaners won't dissolve it.
How to Fix It
You need a degreaser and some patience. Unplug the oven and let it cool completely. 1) Make a paste of baking soda and a little water. 2) Spread it thickly over the hazy glass on the inside. 3) Let it sit for 20-30 minutes to break down the grease. 4) Gently scrub with a non-abrasive sponge or cloth, then wipe clean with a damp cloth. For stubborn spots, a little white vinegar on the cloth can help.
If That Didn't Work
For really tough buildup, use a dedicated oven cleaner, but be cautious. Spray it ONLY on the glass, avoiding any seals, plastic, or the metal frame. Follow the product's instructions precisely, usually involving a short dwell time before wiping.
Heads Up
Never use abrasive scrubbers like steel wool or harsh powders on the glass. You'll scratch it permanently. Also, never spray cleaner directly onto a hot door—the thermal shock can crack the glass.