The navigation symbols are those normally placed at the bottom.

Add a section to table of contents but not to navigation bar

\addtocontents{toc}{\vskip1.5em}
\addcontentsline{toc}{section}{\protect\usebeamercolor[fg]{structure} text}

Remove the navigational circles at the bottom,

\setbeamertemplate{mini frames}{}

References:

[1] How to remove navigational circles and fit the navigation bar titles in Frankfurt beamer theme? - TeX - LaTeX Stack Exchange

[2] Add a section to beamer table of contents but not to navigation bar - TeX - LaTeX Stack Exchange