Can a document that has been published in TUprints be withdrawn or ‘unpublished’?

No, the publication of the thesis is a pre-requisite for receiving the academic qualification. Moreover, unpublishing’ a thesis is practically impossible due to it having been transmitted to other institutions, including the Deutsche Nationalbibliothek. Sect. 19(2)f. of the TU Darmstadt Publication Service Guidelines (opens in new tab) also forbids this practice.