Many people use this font, and I like it too. However, the old typeface is more interesting. xlog cannot import fonts, so I researched how to import remote CSS code.
It's actually just using custom CSS to import, but what I found were all Screen versions, not the TC old typeface version. However, I still found it in this GitHub repository. According to the README, import the TC version and set the font-family to LXGW WenKai TC.
Here is the code:
@import url("https://cdn.jsdelivr.net/npm/lxgw-wenkai-tc-webfont@1.0.0/style.css");
.xlog-page-index, .xlog-page-post {
font-family: "LXGW WenKai TC", sans-serif;
font-weight: normal;
font-size: 18px;
}