In macOS 10.15 (Catalina) and below，The system restricts the installation of non-App Store downloaded applications by default to improve security.。If you need to install third-party software from non-App Store，You can follow the steps below：
How to install non-App Store software
Notice：The following steps only work on macOS 10.15 and below
1. Open System Preferences
Click the Apple icon in the upper left corner of the screen，Then select "System Preferences"。
2. Go into Security & Privacy settings
In the System Preferences window，Click "Security & Privacy"。
3.Unlock settings
In the lower left corner of the Security & Privacy window，Click the lock icon to unlock settings。You will be prompted to enter your administrator password。After entering the password，Click "Unlock"。
4. Allow applications from any origin
In the "Allow apps downloaded from" section，You will see three options：App Store、App Store and identified developers。Select "Any Source"。(Notice：In macOS 10.15 and above，There may not be this option。If this option is not available，Other solutions you can try，To bypass this restriction, use right-click on a file。）
5. Relock settings
Click the lock icon in the lower left corner，to lock settings and protect your security settings。
6.Install software
Now，You can double-click and run apps downloaded from other sources。If you encounter the "Cannot open the application" prompt，Please right click on the application icon，Select "Open"，Then click "Open" to confirm you trust the app。
go through these steps，You can install software from non-App Store in macOS 10.15 and below。
