There are two kinds of offsets: 1. existing offsets where you buy them but there is no net offset creation, 2. newly created offsets where your purchase makes a net difference. An example of (1) could be buying an existing forest that wasn’t going to be felled. An example of (2) could be converting a coal electricity plant to capture CO2 instead of shutting the plant down.

A quick skim of the Apple marketing blurb at least implies they are trying to create new offsets e.g. “Over 80 percent of the renewable energy that Apple sources comes from projects that Apple created”, and “Apple is supporting the development of the first-ever direct carbon-free aluminium smelting process through investments and collaboration with two of its aluminium suppliers.” — https://www.apple.com/nz/newsroom/2020/07/apple-commits-to-b...