Apple has invested in companies before without totally buying them out. Examples include Acorn Computer (now ARM), Akamai, and a $150M investment in Samsung in 1997 to bring down the cost of LCD panels.
Actually didn't invest in Acorn. Apple (mostly just bringing money) along with Acorn (original intellectual property, IP) and VLSI ( a silicon foundry and IP ) founded Arm to make processors. Arm was/is a separate entity from Acorn that was "spun out".
Arm -- processors that Apple was going to use.
Akamai -- web services that Apple was buying in bulk.
Samsung -- LCD panels that Apple is buying in bulks .
All of those are subcontractors for products/services that Apple was constructing. Apple is often Scrooge McDuck when it comes to paying for components/services. So if the contractor needs to do a large capital outlay upfront, then sometime Apple provides the upfront money to get the lower prices. The money is not primarily an investment because Apple wants to tap into the company's general business. It is about buying control for the specific task(s) Apple wants them to do so that Apple can deliver their own product. It far closer to hiring subcontractors than "investing in companies".
Peloton is actually a competitor of Apple (Fitness). Why Apple would spend tons of money propping up a competitor to a service they are still trying to grow to a significant market share? That is all kinds of goofy and lots of hand waving.
Samsung was/is a competitor to several Apple products , but they are a huge conglomerate. They make washing machines , computer chips , refrigerators , cell phone tower radios, ships .... almost everything and the "kitchen sink". If they make something better than everyone else then there is good reason to just deal with the "coopetition/competition" tension.
In contrast, Peloton just made a series of bonehead moves and are stuck with greatly sagging stock price. Most of this "come by 20% of company" is a set of company excutives with deeply 'underwater' stock options and/or shares wanting someone to come in and bail them out. That is about zero benefit for Apple stockholders.
if Apple Fitness was a larger healthy 'core' to augment with Peleton's stuff then maybe. But wrapping fledgling Fitness a round a "lost in the woods" Peloton "core" is pretty dubious. If anything it would be a bigger boat anchor.
Edit: this post is not to say a partial investment in Peloton would be a good idea, just that Apple has done partial investments in the past.
Apple generally does not do "general investing" in other companies due primarily to what the company i doing independent of a direct result for Apple.
https://www.marketwatch.com/story/why-apple-doesnt-have-a-venture-capital-arm-2016-06-15
There are some PR and "grease the political wheels" investments they do ... but that to is mostly to benefit Apple's image.
Apple has nothing equivalent to the historic ATT Bell Labs or IBM Watson Labs.
The bulk of it though is not general investing at all. It is a means to an Apple end. ( acqui-hire to acquire talent. IP buy to acquire something as an internal component , etc. )