According to left leaning media outfits, Brett Baier said so in this interview:

https://kfax.com/columnists/hugh-hewitt/video/66f2afc45ceba70001afa683

The interview itself is ambiguous. What brett said exactly was (among other things)

“The latest is, I actually believe — this is me talking — that the Harris campaign would do a Fox debate, if the former president has come to the conclusion that there really shouldn’t be another debate,” the anchor said.

coverage of interview: https://dailyboulder.com/fox-news-anchor-reveals-trump-not-harris-is-preventing-network-from-hosting-second-debate/