LinkedIn strips most formatting from the first line of a post, which is exactly where bold helps most. Unicode bold characters survive the editor and the mobile feed.
Draft the hook in plain text, run it through Font Style Generator, and paste the result as the first line. Keep the rest of the post in normal characters so the contrast reads as emphasis rather than decoration.
One bold line, one idea. That is the whole trick.
Written by FontStyle - more at fontstyle.io.