AAPL buying/selling itself is a direct link between the assets inside AAPL and its stock price. Money can literally be "put into" and "taken out of" AAPL.
Those "assets inside" AAPL are still dollars. User payed dollars for AAPL share which ended up in a dollar account or a treasury bond. Stop being so obtuse.
Otherwise I can also say the same thing, that you can literally put dollars into Bitcoin by buying GBTC shares, since the dollars become "assets inside" the Bitcoin Investment Trust company.
Sure, the Bitcoin Investment Trust is no different than any other stock. Buying shares of GBTC entitles you to a share of its assets and earnings, same as any other company.
But what are those assets worth? AAPL owns patents, inventory, raw material, real estate, subsidiaries, investments (stocks, bonds, commodities, T-bills, the whole shebang) and straight-up cash. You can add all those together and you can evaluate each of them based on how their value can change over time and under different market conditions.
What assets does GBTC hold? If the answer is "Bitcoin", you've just recursed on "What is the value of a Bitcoin?"; if the answer is "Bitcoin, cash, other cryptocurrencies, and a whole lot of other assets", great, you can evaluate each of them independently and add them all together. But again, you're recursing on the value of cryptocurrencies without really coming any closer to an answer.
I was never discussing what AAPL or Bitcoin is worth or not.
Just the claim that "you can't put dollars into Bitcoin, because there is a seller on the other side which takes the dollars" somehow applies to Bitcoin in a special way. My claim is that this is true for most assets out there, stocks, commodities, or financial contracts.
So let's imagine you buy $1000 worth of AAPL, $1000 worth of pork bellies, and $1000 worth of BTC. Then, simultaneously, AAPL decides to close up shop, no one is interested in buying pork bellies anymore, and the Bitcoin network shuts down.
What do you now own in each case?
AAPL liquidates all of its assets, pays off its debts, and distributes the balance to its former shareholders. You probably don't get $1000, you probably get something like $50 or $100.
Someone delivers some number of physical, frozen pork bellies to you.
And from Bitcoin you get nothing.
This is what I mean when I say all of the buying doesn't actually "put money" into Bitcoin: it is an investment with no underlying value. With all other markets, what you think of as a two-party trade, between the buyer and the seller, is actually a three-party affair, between the buyer, the seller, and the company or asset being traded. "Putting money" into a company ultimately results in that company having more money to build out their business with; "putting money" into a commodity ultimately results in more producers producing more of the commodity. "Putting money" into Bitcoin ultimately results ... in nothing.
That applies to currencies too. I can "put money" into USD (from AUD) which actually does generate X for Y (for example, it creates more purchasing power for all importers in the USA).
Every USD "put into" AAPL is simultaneously taken out by the person on the other side of the trade.
Very few things truly destroy money, and I'm pretty sure all of them are done by banks or treasuries.