Hello,
I just downloaded the latest build 2021.3642 and have similar issue. When I go to “C:\Program Files (x86)\Corona Labs\Corona\Native\Corona\win\bin” and run CoronaBuilder.exe, it said mpc140u.dll not found.
I just copy all DLLs from “C:\Program Files (x86)\Corona Labs\Corona” to “C:\Program Files (x86)\Corona Labs\Corona\Native\Corona\win\bin”. Then re-run the build. Bingo.
Have a try.