cannot open music score 3 on a mac

I need to be able to use muse score for something that was developed by another person for work. I joined for 1 year but cannot open the program...

I'm using a current version of mac IOS (Catalina 10.15.3) yet am told it cannot check for malicious software. I was able to load the program on my ipad but it says to upload a file it needs to be on my desktop.

Please advise