\documentclass[a4paper]{report}
\usepackage{showframe}
\usepackage[many]{tcolorbox}
\newtcolorbox[blend into=figures]{myfigure}[2][]{
center, % <---- this
float=htb,capture=hbox,colback=white,attach boxed title to top center={yshift=-2mm},colbacktitle=white,coltitle=black,boxed title style={size=minimal,toprule=0pt},sharp corners=all,boxrule=0.5pt,enhanced,title={#2},every float=\centering,#1}
\begin{document}
\begin{myfigure}{A tcolorbox figure}
\includegraphics[width=1.2\linewidth]{example-image}