Definitely not. The kernel has its own implementations of any standard C functions which it needs.
Is that because of circular dependencies of glibc on the kernel, or something else?
Circular.
>Is that because of circular dependencies of glibc on the kernel
That but also because lots of code in glibc would simply not work in kernel space
I also stayed away from musl because of compatibility concerns. I see the appeal, and void even has a musl version. But I remember posts about software not being available, maybe sometimes just not being as easy to install. Thinking of steam there for example, though I'm sure there are solutions to make it run anyway.
You can just use flatpacked Steam if you want to use Musl Void. There might be still a few issues, but that's not because of Musl, but because of the Flatpack version.