We're not talking about legal obligations in its home country though. I can buy Jack Daniels at age 19 in my country from their local subsidiary, and no-one thinks that this should be a crime for their US parent company because the US drinking age is higher. (Of course it would be a crime for either the parent or the subsidiary to sell to 19 year olds in the US)
(No-one is blaming Dell or Let's Encrypt here, to be clear, it's the US' excessive extraterritorial laws that are the problem)
At least in Brazil, companies that operate there must obey local laws. What happens when those laws are in contradiction with US laws, like in the example I cited? Is Brazil supposed to cave? Is Brazil supposed to keep fining Dell Brasil until it folds? Maybe prosecute Dell Brasil's directors for actively and repeatedly disregarding the law and fines?
How does that work on a global scale?
I'll say again, this is not about a US company opening a foreign subsidiary to do things in the US that are forbidden in the US. This is about a company incorporated abroad having to follow US laws while operating wholly abroad. This is a breach of sovereignty however you look at it.
Yes, sometimes this causes compliance complication. This isn't unusual, it happens frequently.
Ultimately, every government exercises the laws of their country as they see fit, using the enforcement tools they have available to them. These rules often extend outside of their borders and apply to foreign or partially-foreign entities depending on the situation.
Dell Brazil would have been subject to Cuba sanctions because it was controlled by the US parent company.
Nothing you are are describing is even remotely unique to the US. No country is going to let you set up a foreign subsidiary to launder goods around sanctions law. If they did, everyone would do that and nobody would ever follow sanctions.