Theme: Blue Topaz

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.

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