GFork

You will still see a few promoted pins on the first "page" when loading, but after scrolling and moving around, promoted pins should be removed.

Tested only on Firefox with TamperMonkey while logged into Pinterest. Any other setups may or may not work.

Note: I noticed uBlock Origin now blocks promoted pins using a similar method (filtering XHR json responses), so this userscript might not be needed if you use uBlock Origin.