Is this the first time you are doing an .apk file download?
Could it have landed in the wrong directory on your PC?
Does your PC regard .apk files as dangerous, and not to be downloaded?
Can you do an .apk download from the build of a simple test Project?
Is the Project especially large?
Can you complete an .aia Project Export of your project?
Neither with the button nor with the barcode?
The barcode should download the APK directly to your Android phone.