This superb whiteboard explainer will hash things out for you. But here’s the gist of it:
Ikea Group operates 290 stores across the world.

Ikea Group is owned by Ingka Holding. (So far, that’s a pretty typical company/parent-company arrangement.)

But Ingka Holding is owned by the nonprofit Stichting Ingka Foundation.

The Stichting Ingka Foundation is estimated by The Economist to be even larger than the Gates Foundation, which has $37 billion in its coffers. (The Economist estimated the Ingka Foundation at $36 billion in 2005, but that figure has probably grown.)

Money isn’t trapped inside Ikea’s foundation. The Ikea trademark and concept is owned by another private company, Inter Ikea Systems. So just to operate Ikea stores and use the brand name, the nonprofit has to pay each year—payments that, while obscured by corporate structure, most likely make their way back to Ikea founder Ingvar Kamprad and his family.

Kamprad is a publicly frugal man who despises taxes. He and his Swedish design label actually fled to Switzerland in 1976 to avoid taxes. (Kamprad didn’t deploy his nonprofit scheme until the ’80s.)
In case your palate has been whetted for some corporate conspiracy, the Economist published the foundational investigation on Ikea’s nonprofit tax evasion back in 2005. From what we can tell, it’s still every bit as relevant, because Ikea has only grown bigger since.