Sounds to me like the app has not been codesigned properly therefore Gatekeeper has added a quarantine flag to the extended attributes. It’s Apples security to prevent people from installing an application from an unknown developer, in other words a random application downloaded from the web.
@Freso Whoever develops the Picard application needs an Apple Developer Certificate and to then properly codesign the app before it’s uploaded for users to download. I suspect it was an honest mistake and it was forgotten in the rush to get a release out.
You can use the above xattr -cr command as @SmileyMiley kindly posted above which clears the quarantine flag and recursively clears the flag from all files within the app.
Please read through the following carefully and take your time. As long as you stick to my instructions you will be fine. Hopefully most of you will only have the de-quarantine to deal with. Those on Mojave upwards will have extra steps to take.
Note there is nothing that can cause any harm here as there is no sudo command or entering of any passwords as long you are ether logged in as administrator or have admin privileges. Even if the sudo command was required and entering a password there is still no harm as this is very basic stuff.
To de-quarantine an application launch Terminal which can be found in your Utilities folder.
Type: xattr -cr
Drag and drop the app into the terminal window after the space. This will automatically insert the file path and is simplest method. The above posted if manually typed, /Applications/‘MusicBrainz Picard.app will not work because there is a space in-between MusicBrainz and Picard, it would require a backslash \ in that space. Trust me, just drag and drop and let terminal do the work for you.
You may then have to codesign the application especially if running Mojave and above where notarization comes into play. For this it requires you to install the Apple Command Line Tools which you will be asked to install if not already installed. This may require you to enter your admin password which when asked you will not see as you type in the terminal so you type it blind (no worries with someone looking over your shoulder). Once you have typed the password to install the tools hit return and wait for it to complete
Or you can install them beforehand as follows:
Type: xcode-select --install
You can now codesign the app.
Type: codesign -f -s - --deep
Drag and drop the app into the terminal window
Quit terminal and launch app. Everything should work fine now.
If running Catalina then there are even more security restrictions in place so you may have to temporarily disable System Integrity Protection (SIP) first.
Don’t ask me anything about Windows.