In my opinion, it depends on what your career goal is and what you want out of life.
If you are in a position where you use a technology you don't like or work on projects you don't enjoy, a side project on the weekends can be a way of addressing the gap. Not everyone has the chance of joining a great company.
It also depends on what country or continent you reside in. It appears that in American culture, side projects are actively encouraged; A couple of silicon valley companies have come out of side projects.
A different argument can also be made that doing multiple side projects would not make you a better programmer. Our culture tends to focus on quantitative factors for improving skills rather than qualitative factors. What if rather than doing side projects, one changes ones attitude in their current job? An excellent article on qualitative factors on excellence can be found in https://leveragethoughts.substack.com/p/what-is-excellence