\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\PassOptionsToPackage{natbib=true}{biblatex}
\usepackage{tabularx}
\usepackage{xltabular}

\makeatletter

\makeatother

\usepackage[english]{babel}
\usepackage[style=authoryear]{biblatex}
\begin{document}
The first table is configured as longtable first, the selected variable
length in second column and set the table width 14cm.

\begin{xltabular}[c]{14cm}{|c|>{\centering\arraybackslash}X|c|>{\centering\arraybackslash}X|}
\hline
\hline 
\multicolumn{4}{|c|}{xltabular}\tabularnewline
\hline 
\hline
\endhead
\hline 
 & stretching this column. expecting a line break &  & \tabularnewline
\hline 
Left  &  & Right1 & \tabularnewline
\hline 
 &  &  & and this\tabularnewline
\hline 
 &  &  & \tabularnewline
\hline 
 &  &  & \tabularnewline
\hline 
 &  &  & \tabularnewline
\hline 
\end{xltabular}

The next table is a normal table, variable length of forth column
and width 14cm table with, enclosing paragraph is not indented.

\noindent %
\begin{tabularx}{14cm}{|c|c|c|>{\raggedright\arraybackslash}X|c|}
\hline 
\multicolumn{5}{|c|}{tabularx}\tabularnewline
\hline 
\hline 
 &  &  & stretching this column only, expecting a line break, which comes later.
The table width seems to be wrong & \tabularnewline
\hline 
Left1 & Left2 &  &  & Right1\tabularnewline
\hline 
 &  & Left3long &  & \tabularnewline
\hline 
\end{tabularx}
\end{document}
