Hello Drew, I tried to use ''modeline-region.el'' in emacs 28 and found some inconsistencies due to 
the addition of variables ''mode-line-position-line-format'', ''mode-line-position-column-format'' and ''mode-line-position-column-line-format'' and their use in ''mode-line-position''. Below is a patch which uses the new variables.

BR, Kai

<pre>
diff --git a/modeline-region.el b/modeline-region.el
index 01b8031bf..dc6bfed37 100644
--- a/modeline-region.el
+++ b/modeline-region.el
@@ -1050,7 +1050,7 @@ Sets `mlr--mlp-is-set-up-p' to t, to show the menus have been set up."
                      ((column-number-mode ; Line-number mode & column-number-mode
                        (column-number-indicator-zero-based
                         (10 ,(propertize
-                              " (%l,%c)"
+                              (car mode-line-position-column-line-format)
                               'face (and modeline-region-mode
                                          mlr-column-limit
                                          (> (current-column) mlr-column-limit)
@@ -1059,23 +1059,24 @@ Sets `mlr--mlp-is-set-up-p' to t, to show the menus have been set up."
                               'mouse-face 'mode-line-highlight
                               'help-echo "Line and column, mouse-1: Line/col menu"))
                         (10 ,(propertize
-                              " (%l,%C)"
+                              (string-replace
+                               "%c" "%C" (car mode-line-position-column-line-format))
                               'face (and modeline-region-mode
                                          mlr-column-limit
                                          (> (current-column) mlr-column-limit)
                                          'mlr-column-warning)
                               'local-map mlr-menu
                               'mouse-face 'mode-line-highlight
-                              'help-echo "Line number, mouse-1: Line/col menu")))
+                              'help-echo "Line and column, mouse-1: Line/col menu")))
                        (6 ,(propertize
-                            " L%l"
+                            (car mode-line-position-line-format)
                             'local-map mlr-menu
                             'mouse-face 'mode-line-highlight
                             'help-echo "Line number, mouse-1: Line/col menu"))))
                      ((column-number-mode ; Column-number-mode only, not line-number mode
                        (column-number-indicator-zero-based
                         (5 ,(propertize
-                             " C%c"
+                             (car mode-line-position-column-format)
                              'face (and modeline-region-mode
                                         mlr-column-limit
                                         (> (current-column) mlr-column-limit)
@@ -1084,7 +1085,8 @@ Sets `mlr--mlp-is-set-up-p' to t, to show the menus have been set up."
                              'mouse-face 'mode-line-highlight
                              'help-echo "Column number, mouse-1: Line/col menu"))
                         (5 ,(propertize
-                             " C%C"
+                             (string-replace
+                              "%c" "%C" (car mode-line-position-column-format))
                              'face (and modeline-region-mode
                                         mlr-column-limit
                                         (> (current-column) mlr-column-limit)
</pre>

-- Kai Tetzlaff 2022-03-12 05:31 UTC