XnView MP is now rendering Chinese characters in a legacy font called "Simsun". I believe this is caused by QT's default fallback list on Chinese characters, which I found here:
https://github.com/qt/qtbase/blob/e6693 ... #L810-L859
This is a typical issue in QT programs on Windows.
Can you please make some changes to your QT used, and add "Microsoft Yahei UI" and "Microsoft YaHei" to the top of your list? Now every Windows machine has these fonts installed and they are much better rendering font than Simsun.
If you want a screenshot of current behavior in Xnview, I can attach it here:

Also "无标题" rendered in explorer, using "Microsoft Yahei UI": Thank you.