The base os is immutable, but you can still change configuration files, compile and install local software (but not in the immutable directories), install desktop environment extensions, add custom repositories, etc. You can also layer packages, but most graphical software is best installed as flatpaks (but not mandatory). So it depends on what tinkering means for you. If it means messing around with binaries in the default locations, like /usr/bin, then it’s not for you, but for many other things there is a way, it’s just a matter of getting used to the separation between the immutable base layer and the things that you build around and on top of it.