I’m not sure that it’s possible to track this. Personally I went from probably thousands of dollars a year in 2017-ish to “only after I’ve checked every other store and never a large purchase” today (probably about $150/yr). I never explicitly participated in any boycott, but I’m sure the messages resonated with me and helped me realize I was routinely getting fleeced by Amazon and not the sellers.

It is tricky to boycott Amazon because when I search for a product using Google, I get lots of links to Amazon, and not much else. So I look at the Amazon pages to get search terms and then type those in to other search engines, such as Bing, Brave, or Yandex, and keep going to find online shops. Since Yandex is Russian, I add my country code to my search terms. I also try adding my city name and sometimes find a bricks-and-mortar shop close enough.