I needed to know about the new behavior but was also confused about where to look. To link up some information I found:
The co-scheduling behavior of @async tasks with their parent tasks was discussed in
https://github.com/JuliaLang/julia/issues/41324
For 1.7, it was decided that unsticky tasks become sticky if they launch any children with @async, thus ensuring that @async tasks always run on the same thread as their parent.
https://github.com/JuliaLang/julia/pull/41334
This probably isn’t a long term solution, it’s more of a workaround to ensure existing code doesn’t break.