This is the typical issue you'll always run into when using Common Lisp with
foreign libraries.
I know this very well since I'm working on packaging other Common Lisp programs
like Next browser and cl-torrents.

CFFI is the Common Lisp C Foreign Function Interface.  It looks up libraries in
/usr/lib... by default.  You want to change this path in
`cffi:*foreign-library-directories*`.  Ideally, you would add the canonical path
of all the required libraries there.  If you want to go the lazy way, simply
install the libraries in your user profile and add ~/.guix-profile/lib to this
variable.

Basically all you need is to call

--8<---------------cut here---------------start------------->8---
(ql:quickload :cffi)
(push (format nil "~a/.guix-profile/lib/" (uiop:getenv "HOME")) cffi:*foreign-library-directories*)
--8<---------------cut here---------------end--------------->8---

before calling quickload.
Note that the trailing "/" in the library path is important.

Hope that helps!

-- 
Pierre Neidhardt
https://ambrevar.xyz/