> ;;; In Emacs 28.1, using ':eval' in 'frame-title-format' doesn't work like it
 > ;;; used to in Emacs 27 and earlier. In fact, it is completely broken, if one
 > ;;; uses a frame-parameter in ':eval'.
 > ;;;
 > ;;; The following elisp snippet demonstrates the problem in an Emacs 28.1
 > ;;; instance started with 'emacs -Q'
 >
 > (defun title-suffix ()
 >    (cdr (assoc 'title-suffix (frame-parameters (selected-frame)))))
 >
 > (defvar title-prefix "Test")
 > (setq frame-title-format (list title-prefix '(:eval (title-suffix)) " %b"))
 >
 > ;;; The original frame should show a frame title of 'Test *scratch*'
 > (set-frame-parameter (selected-frame) 'title-suffix "")
 >
 > ;;; The next frame created should show a frame title of 'Test-xxx *scratch*'
 > (make-frame-command)
 > (set-frame-parameter (selected-frame) 'title-suffix "-xxx")
 >
 > ;;; The third frame created should show a frame title of 'Test-yyy *scratch*'
 > (make-frame-command)
 > (set-frame-parameter (selected-frame) 'title-suffix "-yyy")
 >
 > ;;; In Emacs 27 and earlier, that is exactly what happens. Selecting a
 > ;;; different frame doesn't change the titles of all other frames.
 >
 > ;;; In Emacs 28.1, all frames show the same frame title, with the last one
 > ;;; selected determining which one is shown for the bunch of them. Changing to
 > ;;; a different frame changes the titles of all frames to the title of the
 > ;;; newly selected one.

Could you try the attached patch?  Its purpose is to solve a more
general problem in this area and I had to scrape it out from my sources
so there are most likely dragons around.  But AFAICT it does not exhibit
the problem you see, tested with a GNUstep build on old stable Debian.

Thanks, martin