Comment by soneca

Probably worth repeating here an old comment of mine for “side-project” disambiguation.

The term "side-project" has a lot of possible interpretations:

A - Hobby project to play with some tech just because you find it interesting

B - Hobby project to play with some tech that might help your career in the future by learning it

C - Homework project to learn about the tech you currently use at work

D - For-profit project to hopefully earn some extra money on the side and keep it that way

E - For-profit project to hopefully earn enough money that will allow you to quit your day job and make it your main job

F - Portfolio-making projects to show at job-interviews as a junior developer

The OP is about case E apparently (maybe D).