Can you point to an example?

Silica packets are definitely used in foods that need to be kept super-dry, like seaweed or nuts -- absorbing residual moisture that was in the product during packaging.

I've never heard of an oxygen absorber used in food. A lot of snacks and things (e.g. all potato chips) in airtight containers are packaged in nitrogen so there's no oxygen in the first place.

Are they for small-scale food production that can't use nitrogen? I've never encountered them in my life.

The Gimme-brand seaweed snacks I get contain oxygen absorbers. So do packages of Tillamook Country Smoker jerky and meat sticks.

They seem to be fairly common with packages of jerky and other self-stable cured meats.

Bacon bits, fried onions, beef jerky.

I've seen these in imported Asian products, especially from China and Japan. Biscuits and similar dry snacks.

I've never seen it for a European product.

There are both. Oxygen absorbers are used for moist snacks, apparently.