I built 2 popular extensions:

1. Notion Boost: 80K downloads with $10k in revenue

I wrote about my whole journey here: https://gourav.io/blog/notion-boost

2. ChatGPT Writer (https://chatgptwriter.ai) : 700K downloads with $20K MRR

This one I shared on reddit and it grew from there. I will write a post about it soon as well.