You can eat anything, the MC is an omnivore due to their half demon lineage, but it does have consequences.
You could eat that woman’s soul who is walking down the street, but you would have to dispose of the body unless you want the police coming after you and further complicating your life. As a hybrid, you’re limited in the ways you can get a meal.
Fighting, killing, and “eating” other demons is probably the easiest. You won’t face any human consequences, getting a record and/or going to prison, for doing so unless your MC has a guilty conscious about eating former human souls. Other individuals might catch wind of what you’re doing and think you’re doing some good, others might think you’re a cannibal (which you are), and some might try to stop you based on their beliefs. It’s… kinda like hyenas stealing a lion’s hard won kill albeit the digestive process is already done.
In this scenario where you’re hunting your own kind, you’re kind of like the Dovahkiin from Skyrim. Other creatures can kill demons, but it’s not guaranteed that the demon will actually die from their successful attempt. If you go out, kill, and eat a demon, then it’s an assured death.
Hunting down other supernatural creatures may or may not be your second go-to option. Due the demons’ actions of sometimes popping into reality and going on a rampage for something to eat, supernatural creatures are having their own fights to be recognized as people not monsters. As this monster civil rights movement is happening, not all monsters are being considered citizens and thus aren’t protected/granted the rights of a citizen. Meaning, you could go hunt down some werewolves to snack on their souls and you’d have a slimmer chance of going to a trial for killing and harvesting their souls compared to if you hunted and killed humans for their souls. This doesn’t eliminate the possibility of the dog - or in this case, wolf - biting back and hunting you.
As a half human, you can eat human food and it’ll fuel your physical body. It won’t fuel your “demon side” as much as if you went out to eat someone’s soul. Eating human food to fuel your “demon side” is like eating junk food, it’s a cheap and easy fuel source, but it’s not what you need to maintain your health. Eating souls, or stealing another demon’s energy, is eating healthy.