Despite double brackets there is no footer. What could be the reason for this? (Only as a hint: One word in bold works)
Double brackets are not related to footers in SoSci Survey.
I assume, you mixed the manuel for writing content for the manual (https://www.soscisurvey.de/help/doku.php/wiki:syntax) with the manuel for wiki-formatting of SoSci contents (https://www.soscisurvey.de/help/doku.php/en:create:texts#text_formatting).
To make it short: I do not think that footnotes are of any value in questionnaires, and therefore, SoSci Survey does not support any. You can create some via HTML if you like but more likely, you're looking for that: Click to Show Information.
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