It seems to me that you can treat side projects like work, but you shouldn't. Side projects should be about scratching an itch that can't be done at work, whether that is the domain, technology or some other aspect.
If your side project is like work, pick a different side project.
If every side project is like work, as is so for some commenters, then take some time off from them. Or don't do them and forgo the benefits.
https://letterstoanewdeveloper.com/2019/08/02/personal-proje...
It seems to me that you can treat side projects like work, but you shouldn't. Side projects should be about scratching an itch that can't be done at work, whether that is the domain, technology or some other aspect.
If your side project is like work, pick a different side project.
If every side project is like work, as is so for some commenters, then take some time off from them. Or don't do them and forgo the benefits.