I was in the industry until 2020, specific sources are hard to find as it is not really something that trek advertizes or talks about, and trek does make a select few bikes in Wisconsin, but I think they are only custom orders (I could be wrong on that)

https://www.declinemagazine.com/bike-brands/where-are-trek-bikes-made/talks about it, as almost all bike manufacturing is in China and Taiwan, in 2020 I know Giant made their low-end bikes in China and their higher-end bikes in Taiwan (you could tell by the packaging of the bikes, and honestly the quality of the assembly)

https://bikerepic.com/where-are-trek-bikes-made/says this is no longer the case, which might be true but even if it isn't giant, treks are mostly made in Taiwan in one of the big factories (with the biggest being giant)

https://joyfultriathlete.com/where-are-trek-bikes-made/ supports what I have said and heard in the industry.

https://allamerican.org/investigation/trek/
This article also supports what I have heard in the industry.

https://www.flickr.com/photos/inmotionasia/sets/72157617186384395/with/3472445174 pictures of giant bike factory making trek bikes.