Thanks to all respondents, I thumbed through manual. All my questions
relate exclusively to 'reconfigure' and old grub menu entries, and old
system configurations.
guix gc Ok, next:

guix gc -d /gnu/store/kd0nnq3i0qarx4vqxcampxfj3igxn84h-icecat-52.3.0-gnu1
finding garbage collector roots...
guix gc: error: build failed: cannot delete path
`/gnu/store/kd0nnq3i0qarx4vqxcampxfj3igxn84h-icecat-52.3.0-gnu1' since it
is still alive

 - icecat-52.3.0-gnu1 was installed in the first (or second) system
configuration, next 'reconfigure' and 'reconfigure' and 'reconfigure'.. Or
two version of linux-libre - too there is too much :)