How to deal with plagarism from a colleague at another institution?

I’m wondering if anyone has any ideas for how I can approach an ongoing situation.

4 years ago, when I was in the second year of my PhD I attended a conference and, in the normal course of things, I talked about my future dissertation plans with the panel’s chair over drinks after the conference was over. Fast forward to today, and that panel chair, who was writing a dissertation on another subject in another century when we met, has just published a dissertation on that exact same topic, despite the fact that they had never heard of it prior to our meeting (sorry to be so vague but I am, I think understandably, paranoid). My master’s thesis, which is on the same topic, is cited in the dissertation, but there’s otherwise no mention of the fact that they never would have come to the subject without our meeting.

I had caught wind of what was going on a couple of years ago before this person’s disseration was published and approached my advisor about it, but while they were shocked, they recommended just keeping my head down and going about my business. After all, at that point I wasn’t 100 percent sure they would be covering the exact same ground as I was, and seeing as I came to the topic first, the idea was that my work would be superior even if there was some overlap.

Having seen their dissertation (although I can hardly bear to read it, I’m so infuriated) I do think that my work is of far better quality, but this person has hit on several topics, authors, texts, works, etc. that were/are to be central to my own dissertation and I’m wondering if it’s too late for me to try and cry foul somehow.

In order to put my stamp on the topic I have worked to publish parts of my dissertation and recently had an article accepted into one of the top journals in my field. Unfortunately, it will be years before it actually comes out and in the meantime my nemesis is out there on the job market and publishing similar work in lesser, but more time-efficient journals.

I’m aware that this is all sour grapes kind of stuff, but my frustration has gotten to the point where I’m sickly fantasizing about inevitably not getting a job in academia just so that I might have the freedom to call this person out without having to worry about looking unprofessional. In the meantime, though I’m curious to know if there’s a way I could let this situation be known before this person ends up getting that rare prize that is a job on the back of my idea.

Thank you.