Setting \familydefault as \sfdefault is causing the arrow character → to throw Package textcomp Error: Symbol \textrightarrow not provided

The helvet package uses only the characters provided by the original Helvetica that is part of the PostScript default fonts, most of the time via Nimbus Sans (URW Clone). TeX Gyre Heros is an extension of Nimbus Sans that supports the right arrow in text mode. Assuming that the class is actually unrelated to your problem:

\documentclass[12pt,a4paper,english]{article}
\usepackage[utf8]{inputenc}

\usepackage[full]{textcomp}
\usepackage{mathcomp}
\usepackage{tgheros}

\renewcommand{\familydefault}{\sfdefault}

\begin{document}

N → bo.

\end{document}

Result:

Since you are using Debian, you need to have fonts-texgyre installed.

The helvet font doesn't have the arrow. You can change the error to a warning with the warn option. Then textcomp will only add a warning to the log and substitute the arrow from another font. Using tgheros instead of helvet is better:

\documentclass[12pt,a4paper,english]{abntex2}
\usepackage[utf8]{inputenc}

\usepackage[full,warn]{textcomp}
\usepackage{mathcomp}
\usepackage{helvet}

\renewcommand{\familydefault}{\sfdefault}

\begin{document}

N → bo.

\end{document}