1) is not a problem. This is actually already defined technology neutrally in GDPR: "the data subject may exercise his or her right to object by automated means using technical specifications". For specific implementations the law can defer to e.g. standards, as is also very common in legislation.

In general defining laws technology neutrally is bread and butter of legislation, there are just a lot of misconceptions that laws are about specific techniques.

2) you can easily make a non-intrusive UI for that.

Yes, you can make a non-intrusive UI for that. Indeed, website creators can do that right now, with existing technology and compliant with the GDPR as-is.

The question is how do you prevent the annoying UX without making overly technology-specific rules. Just adding a do-not-track header does not stop websites from ignoring the header and showing a pop up to ask you if you want to override your default settings.