How pray tell is the EU going to tell Apple what they have to do in the rest of the world?
If this were found to be a violation of DMA, they could fine them for absurd amounts of money. If Apple paid the fines but didn't fix the underlying issue, they'd be fined even more. After suffient repeat offenses the EU would force Apple to make structural changes such as break up their businesses. If Apple chose to not pay the fines, break up, etc, they would need to stop operating in the EU, or run the risks of their assets being seized, their employees arrested, etc.
It's only at the point where Apple left the EU that there's no more leverage on them. And this is Apple, they're not going to leave a market with money. They didn't even leave China.
(But the real key question is whether there's a reasonable interpretation of the DMA where the companies need to comply even outside of the EU.)
They already do something analogous for taxes purposes.
But the EU can definitely take into account the entirety of Apple when deciding what to do. For example, when Apple gets fined for violating the DMA, the maximum penalties are going to be based on their global revenue, not just the EU revenue going through their Irish subsidiary.
If you're proposing a fully independent public company rather than a subsidiary of Apple, it's true that the separate company wouldn't actually be able to fix any of their possible DMA violations. But that just means they'd not be complying, not that they wouldn't be breaking the law or that they're somehow immune.
Just like the US couldn’t have jurisdiction over a company that only operates in the EU.
Apple could easily not make a subsidiary. But make it a fully independent legal entity that resales in the EU.
Apple can choose not to operate in the EU. That's a totally legit and acceptable outcome. But that means they have to actually give up that revenue. Any attempt at laundering it will just mean that the penalties apply to whatever entity they try to use for the regulatory evasion.
(Or I guess shrink their presence to do small that the DMA no longer applies. But again, this is Apple. They'll rather hand out user data to the Chinese government than leave China and all their juicy money.)
If the EC decides to interpret the rules as requiring compliance globally rather than just within the EU, and the courts were to uphold it, it would be irrelevant that Apple's sales are being done via some shell company. If anything, it would probably be considered worse, since it'd be a clear attempt at circumventing the law. The products that the shell company would be selling would be found illegal, and one way or other the operation would stop. And the effect would be that Apple would have left the EU.
If your plan were actually a thing, every American company would already be doing it just to shield themselves against GDPR (which has fines based on global revenue, not EU revenue). But they don't do it, because it wouldn't work.
What they aren't doing is trying your plan of creating a shell company to break the laws on their behalf.
Not clear though whether they have any interest in doing that.