As a quick workaround, you could wrap `\footcitetext` in `\only<2->{...}`
```
\documentclass{beamer}
\usepackage{csquotes}
\usepackage[sorting=ydnt,style=verbose,autocite=footnote,doi=false,isbn=false,url=false,maxnames=1,giveninits=true]{biblatex}
\usepackage{filecontents}
\begin{filecontents*}{bib.bib}
@article{greenwade93,
author = "George D. Greenwade",
title = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
year = "1993",
journal = "TUGBoat",
volume = "14",
number = "3",
pages = "342--351"
}
\end{filecontents*}
\addbibresource{bib.bib}
\begin{document}
\begin{frame}
blabla \pause
blubblub\footnotemark{} \pause
asdasd
\only<2->{\footcitetext{greenwade93}}
\end{frame}
\end{document}
```
![Screen Shot 2020-03-09 at 10.18.22.png](/image?hash=c956f8cebd26746091598aa83d691e168001357c0584049862d9a769846e7b60)
In case it bothers you that the footnoterule won't be visible on the first slide, this can be solved like this:
```
\documentclass{beamer}
\usepackage{csquotes}
\usepackage[sorting=ydnt,style=verbose,autocite=footnote,doi=false,isbn=false,url=false,maxnames=1,giveninits=true]{biblatex}
\usepackage{filecontents}
\begin{filecontents*}{bib.bib}
@article{greenwade93,
author = "George D. Greenwade",
title = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
year = "1993",
journal = "TUGBoat",
volume = "14",
number = "3",
pages = "342--351"
}
\end{filecontents*}
\addbibresource{bib.bib}
\begin{document}
\begin{frame}
blabla \pause
blubblub\footnotemark{} \pause
asdasd
\only<1>{\let\thefootnote\relax\footnotetext{~}}
\only<2->{\footcitetext{greenwade93}}
\end{frame}
\end{document}
```
![Screen Shot 2020-03-09 at 10.27.04.png](/image?hash=c1871a51cd4bac641e93318fbbefb3260aaeac0cb26558b5520624ae8ca86639)
I know that you would like to keep the footmark/footcitetext combination, but just for completeness a third option that uses `\fullcite` within a footnote. This will ensure the same vertical placement on all slides.
```
\documentclass{beamer}
\usepackage{csquotes}
\usepackage[sorting=ydnt,style=verbose,autocite=superscript,doi=false,isbn=false,url=false,maxnames=1,giveninits=true]{biblatex}
\usepackage{filecontents}
\begin{filecontents*}{bib.bib}
@article{greenwade93,
author = "George D. Greenwade",
title = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
year = "1993",
journal = "TUGBoat",
volume = "14",
number = "3",
pages = "342--351"
}
\end{filecontents*}
\addbibresource{bib.bib}
\begin{document}
\begin{frame}
blabla \pause
blubblub\footnote<2->{\fullcite{greenwade93}} \pause
asdasd
\end{frame}
\end{document}
```
![Screen Shot 2020-03-09 at 13.51.25.png](/image?hash=f3314876df1f4e5a38b7dc0f0ada3f187ebf494c83b8801adc9141a8062360d5)