Sketchbook brushes

Hi everyone

I have sketchbook-pro & I am trying to download the extra brushes manually on my MacBook Air but when I select open the download file to import the brush set the file is greyed out. I call apple support because I thought something wrong with the settings but they checked and said everything in order.

Im suspecting that the download format is not compatible with Mac but I could be wrong. However I am hoping to go get some help from you guys, if any of you encounter the same issue or perhaps overcome this challenge please share your solution or, your IT skills, much appreciated thank you & stay safe.