Check any text against LinkedIn's actual limits: posts, headlines, About sections, connection messages. Live counts as you type. Free, no signup.
Posts cap at 3,000 characters. Headlines get 220, the About section 2,600, a connection note 300, comments 1,250. Articles go longer than any of these. In practice the 3,000 barely matters, since almost nobody hits it. The number that does the real work is the ~210 characters that survive above the fold.
Almost no post fails the 3,000-character cap. What decides performance is the ~210 characters LinkedIn shows before the "...more" fold on desktop (about 140 on mobile). The counter above tracks both, so you can spend your effort where readers actually look.