I made a test doc with formatting: bold, italics, highlights, colored font, embed/transclusion.
I ten exported the doc as a markdown file, which I then opened. Only italics is rendered as such, neither bold, nor highlights nor colored font are rendered.
Inline HTML is not supported, although selecting text produces a pop-up toolbar which does most what I need, but upon export nothing is retained.
This means that, in effect, one is locked in with SiYuan if one does not want to lose formatting. For me this is a deal breaker.
Now, I may well be missing something crucial here, which is why I post this comment because overall SiYuan is a feature-rich, intuitively easy to understand note-taking app that is attractive.