The food example, is the exact reason for large farming subsidies in the European Union. These were implemented as a founding initiative, due to the experience of food shortages during the second world war. A great number of things could be considered critical. Due to the nature of when access could be cut off, the main thing countries likely worry about being able to access, is things humans need to stay alive, and things needed to wage war.

Obviously there are a lot of important things you need to keep a country running, but steel is a key input a in a huge number of very important sectors (infrastructure, military, automotive etc.) so having some ability to produce your own steel seems a sensible hedge.

Food tends to be a lot easier to produce, and many countries do often subsidize their food production, as well as have mercantilistic policies to ensure food production is kept locally.

Vaccines is a more interesting one, and would be something that might indeed be of interest to a nation. On the other hand I don't think many governments are that concerned about another pandemic, sometimes the discourse regarding it very much sounds like "what are the odds it'll happen again"

Steel comes from iron, which you can't grow. It's more critical than food, which you can grow. Same for vaccines.

>Why is steel any more critical than food or vaccines or the like?

Countries that import large shares of their food and medical supply chains are constantly trying to develop domestic capacity.