In 2017 I started writing a GNU/social alternative, when ActivityPub came out in early 2018, I realized I made a big mistake by not handling remote users properly.
I almost gave up, but started researching the most popular social networks.
Facebook, YouTube, Instagram.
I was surprised Instagram was 3rd, and thought that was the easiest to replicate. I joined in 2014 but never used Instagram.
The next day, I started searching for a project name/domain. The .com/.net/.org had to be available.