I found that I was subscribed to 50 users that I didn't remember following (No wonder I'm getting so many notifications!). I looked into the API and found that there wasn't a way to unsubscribe from everyone. No matter, we can do it from the followers list with a little javascript:

document.querySelectorAll(".follow-action-button").forEach(el => el.click())

Run that in Dashboard > following > uers via the console to unfollow everyone. Now you should have a squeaky clean feed ✨ 👍