For a new corporate website we just completed, we used GPC signals as the opt out mechanism. If your browser sends GPC, the site just opts you out of everything and loads zero tracking scripts. If it doesn't, you see a popup that explains how to turn it on if you want, or an "I understand" button.
An approach like this seems ideal to me, the problem is that it's only natively supported in Firefox. Our instructions for Chrome and Edge are basically "install Privacy Badger."
And Safari is the WORST, which as an Apple customer it pains me to say. Not only does the browser not support it, there are ZERO Safari browser extensions, NONE, on ANY platform (mac/iphone/ipad), that you can install that will send a simple GPC signal with the HTTP headers. There is a paid Safari extension on iOS called ChangeTheHeaders that you can configure to send a GPC signal, but come on, you can't ask normal people to buy an app and manually enter a specific HTTP header. (ChangeTheHeaders is made by Jeff Johnson, the same dev as StopTheMadness. I asked him whether he'd consider adding user-friendly GPC signals to that (or any other) plugin and he said it would just be "duplicating functionality" :-/ )