I cannot seem to build a Milling Machine in my Windmill. I have only tried it this once as I'd rather not lose the resources if possible. This is the first time I've tried to build the Milling Machine, I did build a Sawmill on the same floor as you can see in the screenshot. The 2nd floor is empty, and the top floor just has a study desk on it.
When I try to build the Milling Machine I get the message: "The mill needs to be built in a place with available mechanical power." This is after the construction sign has already accepted all of the resources for it.
I did see this posted back in 2021 but it didn't have any resolution.
It it matters at all, I did have the construction sign up for quite some time with only some resources on the site, but I just had enough excess bone glue to finish the build.