--- /usr/lib/ubiquity/ubiquity/frontend/kde_ui.O.py	2023-01-10 08:26:07.000000000 -0800
+++ /usr/lib/ubiquity/ubiquity/frontend/kde_ui.py	2023-04-24 19:54:51.660054461 -0700
@@ -532,6 +532,17 @@
         if self.current_page is not None:
             self._update_breadcrumbs('__install')
             self.start_slideshow()
+            # At this point, it does not make sense to show the Back & Next
+            # buttons anymore. Besides, a click on the Next button would make
+            # the application crash.
+            # In most scenarios, the call to self.start_slideshow() is enough
+            # to hide the navigation. Having said that, the function does not
+            # hide the navigation if:
+            #  * the slideshow does not exist ; which is the case when running
+            #  oem-config (see LP #1990196)
+            #  * if the slideshow is disabled intentionally through debconf
+            #
+            self.ui.navigation.hide()
             self.run_main_loop()
 
             telemetry.get().done(self.db)
@@ -1069,8 +1080,13 @@
         if not self.allowed_change_step or not self.allowed_go_forward:
             return
 
+        # Ignore page where index does not exist.
+        try:
+            ui = self.pages[self.pagesindex].ui
+        except IndexError:
+            return
+
         self.allow_change_step(False)
-        ui = self.pages[self.pagesindex].ui
         if hasattr(ui, 'plugin_on_next_clicked'):
             if ui.plugin_on_next_clicked():
                 # Stop processing and return to the page.