I pushed the addition of linux-libre 5.11 to the kernel-updates Git
branch:

https://git.savannah.gnu.org/cgit/guix.git/log/?h=kernel-updates

And CI is building it (the x86_64 is already built and the i686 kernel
should be done in about an hour):

https://ci.guix.gnu.org/jobset/kernel-updates

Feel free to test and provide feedback! Since the 5.10 kernel is still
the default, you'd need to put (kernel linux-libre-5.11) in your
config.scm.

I'll keep linux-libre-5.10 as the "default" kernel until stable releases
of 5.11 start being released, but we can add 5.11 in the next day or
two.