We received one bug report about XeTex, the variable fonts is not usable with xelatex.

The original bug report and example file is in the following line.
URL: https://bugzilla.redhat.com/show_bug.cgi?id=2271559

From the report, xelatex got the following error with variable fonts:
xdvipdfmx:fatal: Invalid TTC index number

No output PDF file written.

Reproducible: Always

Steps to Reproduce:
1. Install google-noto-sans-cjk-vf-fonts, and google-noto-sans-mono-cjk-vf-fonts, as well as texlive packages necessary for xelatex including texlive-xetex and texlive-ctex
2. Run "xelatex test.tex", with test.tex shown below

test.tex
-------------------------------------------
\documentclass{article}
\usepackage{xeCJK}
\setCJKmainfont{Noto Sans CJK SC}
\setCJKmonofont{Noto Sans Mono CJK SC}
\begin{document}
中文 \LaTeX 示例。

{\ttfamily
中文 \LaTeX 示例。
}  
\end{document}
-------------------------------------------
Actual Results:  
xelatex+xdvipdfmx ends up in an error:
-------------------------------------------
xdvipdfmx:fatal: Invalid TTC index number

No output PDF file written.
 )
Error 256 (driver return code) generating output;
file test.pdf may not be valid.
Transcript written on test.log.
-------------------------------------------

Expected Results:  
The PDF file is written correctly.