I was about to reply to this thread, but it's auto closed so I think sharing here might help as well.
- Get note link by right clicking on note list item, then select "Copy markdown link"
- Just take the url part in link obtained from 1, then change the suffix to "joplin://"
- Then apply the link as instructed in mermaid docs
- The emoji in the pic above is just a hint for myself
Courtesy of discussion in this thread