Please help us help you and fill where relevant:
Your LimeSurvey version: Version 5.3.11+220425
Own server or LimeSurvey hosting:
Survey theme/template:
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Dear Forum,
I know this has been a common topic, and some may not like this question type, but we want to add a free text field to an matrix question, nevertheless. It does not seem to be working in Version 5.3.11 +
We disabled "Filter HTML for XSS" and tried several scripts posted here, for example: 
forums.limesurvey.org/forum/design-issue...-text-for-one-option
We tried it online on limesurvey and offline on a local computer.
What could be the issue? Many thanks in advance!

This is a little bit like calling your car mechanic and say: My car doesn't start. I have tried a few things, but nothing helps. What could be the problem.

Add a LSS export with just the relevant parts that show what you have tried.

Of course it works in 5.3.11.
 

As @holch.
If you do not show what you tried, we do not know what was wrong.

Sorry, of course:


Any help is much appreciated!

Hi,
I do not see anything that would make it work.
Did you import the example in the link you provided.
This example is for array(numbers)
But you obviously aree using an array. This is different.

 

As you seem to speak German, I recommend my tutorial
"Joffms Tutorial 1: Matrizen", Chapter 3.2.
In the German part, at the moment on page 3, I think.

Joffm
 

Thank you so much for your great tutorial! It works!
It's a shame LimeSurvey is not able to officially provide sth. like this...

It's a shame LimeSurvey is not able to officially provide sth. like this...

Resources are usually very limited in OSS projects.