\documentclass[serif]{beamer}
\usepackage{tikz}
\usepackage{amsmath}
\begin{document}
\begin{frame}{Adam Optimizer}
Initialize ...
Parameter $\beta_1$ is usually 0.9.
Calculate momentum
$$ a=b $$
Calculate velocity
$$ b=c $$
\onslide*<2>{
\begin{tikzpicture}[overlay]
\node {hello world};
\end{tikzpicture}
}
\onslide<3->
Then we have ...
\end{frame}
\end{document}
From slide 1 to slide 2, the text shifts up a bit. How to fix this?
Is the tikzpicture with overlay option still somehow occupy space?
I also tried to change \onslide*<2> to \onslide<2>, then the text doesn't shift, but the space between b=c and Then we have ... is enlarged.

%right after\onslide*<2>{and another one after\end{tikzpicture}with no spaces before the%. – Nov 24 '20 at 16:44}and after\onslide<3->. Then it's fixed. – Gqqnbig Nov 24 '20 at 17:05