Authenticity is not a personality. It is a strategy, and it has to come first.
Most professionals in a second act do the reverse. They pick a format, a posting rhythm, or a niche label, then try to sound like themselves inside it. The work comes out polished and slightly false. The people who would hire you can hear that. They have sat through enough presentations.
Start with the sentence only you can say. One problem you have handled more than once. One judgment call you would still make. One thing you will not pretend. Record or write from that, before you worry about the thumbnail, the hook, or the offer.
Authentic first does not mean unedited. It means the edit serves the truth instead of sanding it down. Cut the preamble. Keep the specific. Leave in the part where you were wrong the first time. That is the material a serious person trusts.
The strategy is simple. If a former colleague would recognize the story, publish it. If it could have been written by anyone with a course, do not. The channel, the posts, and the practice all get clearer once that filter is in place.
What is one thing you know from the work that you have been softening so it will sound more acceptable?