Question on validity of Dua Khatm within Salah

It is the practice of many Imams in Ramazan that when they finish the recitation of Surah Naas (in Taraweeh, not Witr), they immediately begin the Duaa of Khatm before Rukoo’. Is this something that will be allowed in the Hanafi school? I was under the impression that making sort of any sort of Duaa in the Qiyam position will invalidate the Salah besides the Fatiha.

Also, is there any sort of precedent for those who practice this method? I’ve read some Hanbali texts that mention this practice without any evidence for it.