Files inside the guix store are read only. "styles.xml" is copied from the
store (/share/emacs/26.3/etc/org/OrgOdtStyles.xml), so it's read only too.
ox-odt needs this file, so if it's not writable it will fail. This patch
adjust the permissions.

---
 lisp/org/ox-odt.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/org/ox-odt.el b/lisp/org/ox-odt.el
index f9c4a93cc8..61988ffcc4 100644
--- a/lisp/org/ox-odt.el
+++ b/lisp/org/ox-odt.el
@@ -1384,6 +1384,8 @@ original parsed data.  INFO is a plist holding export options."
     ;; create a manifest entry for styles.xml
     (org-odt-create-manifest-file-entry "text/xml" "styles.xml")
 
+    ;; guix store files are ro. This file need to be modified, make it rw
+    (set-file-modes (concat org-odt-zip-dir "styles.xml") #o600)
     ;; FIXME: Who is opening an empty styles.xml before this point?
     (with-current-buffer
 	(find-file-noselect (concat org-odt-zip-dir "styles.xml") t)
-- 
2.24.0