Thanks. It was reasonably easy to to fix. See
commit e6f3a4dc6cd4ffca9b8b2ea0c9271f832df07e3e (HEAD -> master,
origin/master, origin/HEAD)
Author: João Távora <joaotavora@gmail.com>
Date: Sun Aug 15 09:12:23 2021 +0100
Fix bug#50063 when using icomplete-fido-kill with C-x p p
C-x p p utilizes a completion table "category" which is 'project-file'
icomplete-fido-kill only functioned for 'buffer' and 'file', and
failed with a non-informative message when something else was used.
* lisp/icomplete.el (icomplete-fido-kill): Support 'project-file'
class. Use cl-case, instead of pcase.