The opposite: it's mandated that you not do data collection and tracking for reasons except those essential for the company to provide the product or service, absent informed consent. (And this is purely for tracking: cookies used for maintaining preferences or other state are fine.)

The banners are a fig leaf for behavior that violates the spirit of the GDPR, creating an aggravation where the simplest way to dismiss them is by agreeing.

Any site that doesn't offer a button to reject the tracking (with no more stops than angreeing) and still function as expected without the tracking, is in violation of the law.