I'm fairly new to the game, but I'm a solo developer. Currently I dont make enough to quit my day job, but it is a nice supplementary income, and it's nice to get paid a bit for something I truly enjoy.

There are also several solo/small shop developers that do make a living from selling plug-ins. Here are a few that I can think of off the top of my head.

Auburn Sounds: https://www.auburnsounds.com/ Valhalla DSP: https://valhalladsp.com/ Kilohearts: https://kilohearts.com/