Population III stars constitute the first generation of stars that appeared after the Big Bang (https://en.wikipedia.org/wiki/Stellar_population#Population_III_stars). So far none of these stars were found.
Will at least one Population III star be detected by JWST by the end of 2026?
The market will resolve to YES if the detection is published in a peer reviewed journal or if it is published as a preprint and not refuted within the next month.
Disclaimer: I will not bet on the market.
Apparently there have been some studies claiming evidence for Pop 3 stars: https://arxiv.org/pdf/2306.00953.pdf, YouTube video describing the evidence: https://youtu.be/UA-He0aIbJc.
I don't think this by itself resolves this market, since so far this is only an indirect evidence and the market description mentions "at least one star", implying that a separate star should be detected. But I'm open to the discussion.