How can I avoid that vskip after {equation} and after {enumerate} add up?

Question

After an enumerate item, latex leaves a vertical space.

After an equation, latex leaves a vertical space.

If the equation is the last line in an enumerate environment, latex adds both vertical spaces.

How can I tell latex to leave out the smaller of the two vertical spaces?

Edit: To answer the remarks, I use

\usepackage{enumitem}   
\setlist[enumerate]{%
        leftmargin=15mm, 
        rightmargin=0mm,  
        labelwidth=13mm,  
        labelsep=2mm, itemindent=0mm, itemsep=0.0mm, 
        topsep=0mm plus 2mm}

and in the file

Text...
\begin{enumerate}[resume]
   \item  More text...
   \begin{equation}
    a^2+b^2=c^2  \;\;.
   \end{equation} 
\end{enumerate}
Even more text ...

It might well be that the \topsep command has reduced the upper spacing, and that one or two similar commands need to be added at the bottom, one for the enumerate and one for the equation.

In any case, the vertical spacing above the \item is much smaller than between the bottom and the "Even more text ..."

Remark: also setting

\setlength\belowdisplayskip{0ex}
\setlength\belowdisplayshortskip{0ex}

does not change the fact that in displayed equations inside normal text, the spacing above and below is ok. But when an equation is at the end of an item, the spacings below the equation at the end of an item and above the item differ.

Here is a simple file that shows the problem:

\documentclass[onecolumn,nofootinbib,aps,prd,preprintnumbers,11pt,longbibliography,floatfix]{revtex4-2}

\usepackage{enumitem}  
\setlist[enumerate]{label={\hbox to 13mm{%
        \hbox to 0mm{\small\sf\textbf{Nr.}~\small\sf\textbf{\arabic{enumi}:}\hss}%
           \hfill}},%
        leftmargin=15mm,  
        rightmargin=0mm,  
        labelwidth=13mm,  
        labelsep=2mm, itemindent=0mm, itemsep=0.0mm, 
        topsep=0mm plus 2mm}  
        
\renewcommand{\baselinestretch}{1.1}
\normalsize

\begin{document} 

Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
\begin{enumerate}
    \item  
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
\begin{equation}
a^{2}+b^{2}=c^{2}.
\end{equation}
\end{enumerate}
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.

\end{document}

The vertical spacing above the "Nr. 1" is much smaller than below the equation.

Answer 1

You're forgetting to set \parsep to zero.

The label can also be simplified; and ref should be set.

\documentclass[
  onecolumn,
  nofootinbib,
  aps,
  prd,
  preprintnumbers,
  11pt,
  longbibliography,
  floatfix
]{revtex4-2}

\usepackage{enumitem}  

\setlist[enumerate,1]{
  label=\small\sffamily\bfseries Nr.\ \arabic*:,
  ref=Nr.~\arabic*,
  align=left,
  leftmargin=15mm,
  rightmargin=0mm,
  labelwidth=13mm,
  labelsep=2mm,
  itemindent=0mm,
  itemsep=0.0mm,
  topsep=0mm plus 2mm,
  parsep=0pt,
}
        
\linespread{1.1}

\begin{document} 

Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
Some text. 
\begin{enumerate}
    \item  
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
    This is also text. 
\begin{equation}
a^{2}+b^{2}=c^{2}.
\end{equation}
\end{enumerate}
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.
More text.

\end{document}

Aside, the command \sf, together with almost all two-letter font changing commands (excluding \em) have been deprecated for about 30 years.