How are you trying to download the apk? Are you using Build > App (provide QR code for apk) or Build > App (save .apk to my computer)? The first choice provides a QR code to be used with your device to install the apk; the second choice downloads the apk to your PC Downloads folder.
Do you get an error message or is this an issue of you cannot find the downloaded apk on your Windows 10 PC? If you see an error message, what is the message?