Docker's implementation is instant if you accept, but takes an eternity if you only want essential cookies. That seems in violation of the ePrivacy directive which according to the official website [1] requires that you "Make it as easy for users to withdraw their consent as it was for them to give their consent in the first place."
I guess it's for the courts to decide if requiring the same number of clicks but letting you wait for an eternity is equally easy, but I doubt it.
The problem is that it takes so long because they make a bunch of requests to the opt out endpoints of different services, which takes time. Of course, it is questionable why those requests are essential, but the point is that there is a reason to this madness.
But why do they block user interaction while doing that? You can call those in the background.
And why call an opt-out endpoint at all, after all there has to be a mechanism that prevents setting the cookie before the user sees the cookie banner. Just continue using that mechanism (e.g. gtag's consent default denied).
I guess it's for the courts to decide if requiring the same number of clicks but letting you wait for an eternity is equally easy, but I doubt it.
1: https://gdpr.eu/cookies/