Skimming through this forum as well as the current documentation of biblatex, I did not find a functionality to achieve this. First, consider this MWE, inspired by this answer here:
\documentclass{article}
\usepackage{biblatex}
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@misc{FirstEntry,
author = {Author, A. and Donald Duck and Winston Churchill},
year = {2010},
title = {Some Title},
}
@misc{SecondEntry,
author = {Buthor, B.},
year = {2020},
title = {Another Title},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\nocite{*}
\begin{document}
\textcite{FirstEntry} \textbf{shows} us nothing at all.
\textcite{SecondEntry} shows us a lot.
\printbibliography
\end{document}
yielding
From the biblatex doc, we see that textcite is provided as \textcite[<prenote>][<postnote>]{<key>}, working wonderfully. Now, this is a very minute and niche thing to ask, but is there a function like
\textcite[<prenote>][<postnote>][<base verb>]{<key>}
essentially expanding the command by another optional argument that takes in the base form of a verb, and prints, e.g., do if the textcite and its surrounding settings happen to print a list of authors, like for FirstEntry in my first example, and does if it so happens to print a single author?
It is easy to do this manually. However, it is sometimes not obvious, especially if working with external library software like Zotero, if a bib-entry has just one or multiple authors. This has happenend to me many times now, and if at some point one overlooks the tiny missing (or superfluous) s at the verb's end, it can get embarrasing.
We could then use
\textcite[][][show]{FirstEntry} us nothing at all.
\textcite[][][show]{SecondEntry} us a lot.
and never have to worry again, since it would do nothing to the base verb in the first sentence, and automatically append the s in the second one.
If the authors of the bib entry change later, after the respective passage has long been written, we would not have to worry about that either.
This is also thinkable for other languages.

\textcite[][]{SecondEntry}[<verb>], which would at least not deteriorate the source's readability imo. But seeing the level of 'intervention' required as per @samcarter's link, I decided against using it. It seems like too much of a hack. There is likely good reason it is not a feature. – Alex Povel Jan 13 '19 at 15:41