I've tried the installer today and it failed at the wifi selection,
printing a stack trace which allowed me to investigate.  Since I could
not save it (shouldn't we dump it to a file by the way?), I've noted
down the following, roughly:

--8<---------------cut here---------------start------------->8---
In /gnu/installer/newt/wifi.scm:
  204: (run-wifi-page)
       (filter ...:145 (service)...
       (#<<service> name: "foo" type: "wifi" path: "wifi_d..." ...)
  147: (_ #<<service name: #f ...)
       (string-null? #f)
--8<---------------cut here---------------end--------------->8---

Apparently it fails because a wifi service name is #f.

I can think of two fixes (untested).  In wifi.scm:

--8<---------------cut here---------------start------------->8---
@@ -144,6 +144,7 @@ of <service-item> records present in LISTBOX."
   (let ((services (connman-services)))
     (filter (lambda (service)
               (and (string=? (service-type service) "wifi")
+                   (service-name service)
                    (not (string-null? (service-name service)))))
             services)))
--8<---------------cut here---------------end--------------->8---
 
Or, more directly in connman.scm:

--8<---------------cut here---------------start------------->8---
@@ -108,7 +108,8 @@
 (define-record-type* <service>
   service make-service
   service?
-  (name            service-name) ; string
+  (name            service-name
+                   (default ""))
   (type            service-type) ; string
   (path            service-path) ; string
   (strength        service-strength) ; integer
--8<---------------cut here---------------end--------------->8---

Thoughts?

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