Guys, I run the latest LimeSurvey Cloud Version 5.2.4.
I see the layout is changed slightly.

Where does one set up Default Values these days?
The sitting used to be at the top (screen below). Yet it isn't there any more ... I'm clearly missing something.

 

Edit default answers is still there, even in your screenshot...

What question type?

Oh sorry, blond moment. The first screen shot does show it indeed.
The question type in question is Array (Texts). I don't think that one has the same Default Answers option. Screen attached. 
 

I don't think that the question type "array (Texts)" ever had a default answer option. Are you sure it had a default answer option before? I just checked and in LS 3.27.26+211123 this question type also has no default answer option.

I think you might be able to use a equation question on a page before to set the default values via expression manager.

With something like this you can apply a default value for each text field in the array (text) question type, as long as the equation question is before the question or at least on the same page, I guess.

Thank you so much, holch.
It works 100% when I use {C10_SQ001_SQ001 = S6_SQ001_SQ001}

But the moment I start adding more raws using the AND operator, it stops working unfortunately. Example:
{C10_SQ001_SQ001 = S6_SQ001_SQ001 AND C10_SQ002_SQ001 = S6_SQ002_SQ001}

Please will you point me in the right direction one more time? Again, thanks so much in advance!!

UPDATE:
I've fixed it. The right format is below:

{C10_SQ001_SQ001 = S6_SQ001_SQ001}, {C10_SQ002_SQ001 = S6_SQ002_SQ001}

I've fixed it. The right format is below:

{C10_SQ001_SQ001 = S6_SQ001_SQ001}, {C10_SQ002_SQ001 = S6_SQ002_SQ001}

Exactly!