'Don't reinvent the wheel' is a big reason I've put off almost all side projects that I've wanted to do. Everything I've thought of, someone else has already written, and it's quite demoralising. I end up thinking, 'what's the point?'
If you cannot yourself come up with a truly original idea, consider this; There is always the opportunity and option to do a thing better than it's been done before. Choose a thing that excites you, but you see possibilities for improvement, or a unique way of doing it that may be better than those who have gone before. "Stand on the shoulders of giants" if that benefits you, but do it in the way that only you can do.
If you can't reinvent the wheel on company time, I would urge you to try and do it on your own time. You don't necessarily have to use the solution you come up with, but it helps to get a deeper understanding of the code beneath the libraries you use. Using this technique definitely made me a better developer when I was younger. I still like to take small portions of libraries I use and try to code them myself, just to get a better feeling for how things work (even if the code is vastly different from the library I use).
Heh, I wish I had 'company time'. I am a final-year undergraduate with a mediocre GPA and no job offers. Ergo all my time is 'own time', and most of what I do is interview preparation by grinding Leetcode problems.
