Yes, the US is purposely starving the world.

Yep. I doubt you'll care to read the following but I'm putting it here for others to see.

The United States is the world leader in imposing economic sanctions and supports sanctions regimes affecting nearly 200 million people. ... Targeted countries experience economic contractions and, in many cases, are unable to import sufficient essential goods, including essential medicines, medical equipment, infrastructure necessary for clean water and for health care, and food. ... While on paper most sanctions have some humanitarian exemptions for food, necessary medicines and medical supplies, in practice these exemptions are not sufficient to ensure access to these goods within the targeted country. (Center for Economic and Policy Research)

It's well known that sanctions are ineffective for pressuring governments, but very effective at waging siege warfare by starving and killing ordinary citizens by disease and infrastructural failures. Continuing to use sanctions in this way and to this extent, when this is well known, is definitely "purposely starving the world". An independent expert appointed by the Office of the High Commissioner for Human Rights said in 2019 that US sanctions violate human rights and international code of conduct and can lead to starvation. Why does the US continue to be the world leader in imposing sanctions, increasing its use of sanctions by 933% over the last 20 years, when this is well known? It's because they know the effect, and they're doing it on purpose.

We can also look at some US internal memorandums from before it was more politically incorrect to talk about starving people in other countries. In 1960, U.S. officials wrote that creating "disenchantment and disaffection based on economic dissatisfaction and hardship" through denying money and supplies to Cuba would be a method they should pursue in order to "bring about hunger, desperation and overthrow of government" in Cuba.

In other countries, we see a pattern of US officials and US-backed institutions purposely denying aid and loans to governments they don't approve of, and then suddenly approving aid and opening up loans when a coup brings a leader they're happy with into power. When Ghana was requesting aid under an administration that the West's bourgeoisie didn't like, U.S. officials said this: "We and other Western countries (including France) have been helping to set up the situation by ignoring Nkrumah’s pleas for economic aid. The new OCAM (Francophone) group’s refusal to attend any OAU meeting in Accra (because of Nkrumah’s plotting) will further isolate him. All in all, looks good." The "situation" they were helping to set up was a coup they knew was going to happen. After a US-friendly coup took place, suddenly it was time to give the "almost pathetically pro-Western" government a gift of "few thousand tons of surplus wheat or rice", knowing that giving little gifts like this "whets their appetites" for further collaboration with the US. You will find the same song and dance in numerous other countries, Chile being a well-documented example, if you simply look for it.

The US imposes starvation and depravation of other countries on purpose, using it as an economic wrecking ball, then pats itself on the back for giving "aid" to the countries which have been hollowed out by such tactics.

The loans which magically become available to countries that meet the US approval standards are not so pretty either, as a former IMF senior economist said, he may only hope "to wash my hands of what in my mind's eye is the blood of millions of poor and starving peoples", there not being "enough soap in the world" to wash away what has been done to the global south through the calculated fraud of the IMF, whose tactics are designed to accomplish the same kind of goals as the sanctions are--to prevent the economic rise of any country but the US by wrecking its competitors economically, tearing apart their local manufacturing capacity and transforming them into mere resource extraction projects, redirecting their agricultural industries into exports to make sure they reach a level where they are more reliant on imports to feed themselves, and reliant on foreign aid which is ripped away whenever they do not do what the US approves of or make friends with who the US wants them to.

I refer to #3, why don’t they just do it then?

This is what secondary sanctions and the US's various protection rackets have always been designed to prevent, which has definitely been a powerful tool for them, but it seems with the rise of the new non-aligned movement and de-dollarization its becoming a less successful one and we can see countries "just doing" what they want more and more while the US leadership waves around, as usual, more sanctions and military threats in response.