okay I've got a fix, but I have no idea how to get the fruity_twentythree theme to build properly
the repo doesn't have a lock file, I tried working backwards to generate it, and it's close, but it's not quite right.
I'm still getting lots of changes to the built theme besides the changes I made to the unbuilt theme. also I suspect there is some other process that runs afterwards that changes whitespace.
i'm attaching a patch, maybe someone that has the correct deps can build and make pr
i'm so many hours into this over such a simple changeset...

i think if someone has the yarn.lock that would help a lot

diff --git a/assets/survey_themes/fruity_twentythree/core/old_core_theme.js b/assets/survey_themes/fruity_twentythree/core/old_core_theme.js
index 67cf09cc39..4d0731eceb 100644
--- a/assets/survey_themes/fruity_twentythree/core/old_core_theme.js
+++ b/assets/survey_themes/fruity_twentythree/core/old_core_theme.js
@@ -21,9 +21,13 @@ export var ThemeScripts = function () {
     /**
      * fix padding of body according to navbar-fixed-top
      * in endpage and in $(window).resize
+     * also fix the max height for the dropdown menu as it depends
+     * on the same value
      */
     var fixBodyPadding = function fixBodyPadding() {
-        $('body').css('padding-top', Math.round($('#survey-nav').outerHeight()) + 'px');
+        var navHeightPx = Math.round($('#survey-nav').outerHeight());
+        $('body').css('padding-top', navHeightPx + 'px');
+        $('#main-dropdown').css('max-height', 'calc(100vh - ' + navHeightPx + 'px)');
     };
 
     /**
diff --git a/assets/survey_themes/fruity_twentythree/navbar/navbar.scss b/assets/survey_themes/fruity_twentythree/navbar/navbar.scss
index f69ed541a4..7ff9d279b3 100644
--- a/assets/survey_themes/fruity_twentythree/navbar/navbar.scss
+++ b/assets/survey_themes/fruity_twentythree/navbar/navbar.scss
@@ -117,6 +117,9 @@ Responsive navbar-brand image CSS
 
     #main-dropdown {
         min-width: 250px;
+        max-width: 100vw;
+        overflow-x: auto;
+        overflow-y: auto;
     }
     .dropdown-header {
         font-weight : $font-weight-500;

@p_teichmann

you added the last commit, do you have build dependency info? or do you still have the same set of dependencies installed and can build from my patch?

@mfavetti Hey, the build dependencies can be a bit confusing since we are not correctly using it. The way how we do it internally to get the correct state is, delete the contents of the node_modules folder, then do a git reset --hard to get some hardcoded files (which is not great). Afterwards do a yarn install and you should be good to go.
We intend to fix the hardcoded parts, but currently we are short on time.

@p_teichmann
Okay, I followed your instructions. This is still not ideal. There are a lot changes to CSS replacing -webkit-margin-end and margin-inline-end with only margin-inline-end and other similar stuff. Also a ton of JS changes beyond what I touched.

Do you git add -p and only accept the modifications related to the changes to the base files? Or something like that?

I added a PR but I DO NOT think it should be merged as is. I added it mostly to get feedback on how to get the build to be correct.

Steps I used:

1. Clean checkout of latest master
2. rm -rf node_modules
3. git reset --hard
4. yarn install
5. git apply issue19250.patch
6. gulp build_survey_theme_ls6
7. git add .
8. git commit

Maybe I need to do git add -p . and only add the changes directly related to the patch????

It can happen if some of the node modules versions changed, i would not worry to much about this since it is only the build step and has pre-configured options which might affect how the compiled code looks in the end depending on global browser version usage.

The changes in the files are in line with what i would expect and also get myself locally.