Dump the can of tomatoes into the pot, but don't stir it in. Leaving the tomatoes on top reduces the chances of getting a burn error.
1 14 ounce can diced tomatoes
Seal the lid and pressure valve and cook on high pressure for 10 minutes. It will take about 10 minutes for it to reach pressure.
Manually release pressure by flipping the valve open and stir in the shrimp. Put the lid back on and let it sit for 5 minutes to heat the shrimp.
12 ounces small shrimp
Sprinkle with green onions and serve over rice.
Notes
If you want a darker roux (which is traditional for gumbo) you can cook it for longer, up to 30-45 minutes.You can't control the saute function temperature on an Instant Pot, which means it might cook the roux at a higher temperature than is ideal. If you really care about getting a perfect roux I suggest cooking it in a pan on the stove where you have more temperature control.I make and test my recipes in a 6 quart Instant Pot. Another brand or size of pressure cooker might affect your results.