I have this customisation

(setq dired-guess-shell-alist-user '(("." EXP)))

where EXP evaluates to a list of strings. It has been working for ~10
years until Emacs 28.

After some digging it turns out there is a rewrite of
`dired-guess-default' which is not compatible. Previously returning a
list of strings from EXP accidentally worked.

  (eval (car cmds) `((file . ,file)))  ; single command

but if it evaluates to a list of strings it is perfectly fine as per the
documentation of dired-guess-default. I propose the following patch for
remedy.