It may well be due to these 2 code blocks:
.markdown-preview-view.is-readable-line-width .markdown-preview-section,
.markdown-source-view.is-readable-line-width .CodeMirror,
.markdown-preview-view.is-readable-line-width .markdown-preview-sizer {
line-height: 30px;
font-family: var(--font-family-major);
text-align: justify;
}
/*preview line height*/
p {
line-height: 1.7;
text-align: justify;
}
which show the text alignment is justified.
You could copy these to a snippet and set the text alignment to “left” (w/o quotes).
Remember to enable the snippet.