New versions of Netbeans don't propose Netbeans 8.2 plugins portal by default, it must be added manually :
Press Add button
Netbeans 8.2 plugins portal
https://updates.netbeans.org/netbeans/updates/8.2/uc/final/distribution/catalog.xml.gz
If you use one of the latest openJDK (as you should), it doesn't provide unpack200 that will be requested to install C++ plugin.
You MUST have an older version of the openJDK installed (8, 11 or 13) to find them (or find the binaries and copy them on your system.
When you will restart Netbeans to install the C++ plugin, a Window will popup to say that it needs to find unpack200
For example you can find it here, on Ubuntu :
/usr/lib/jvm/java-1.11.0-openjdk-amd64/bin (symlink)
/usr/lib/jvm/java-11-openjdk-amd64/bin
New versions of Netbeans don't propose Netbeans 8.2 plugins portal by default, it must be added manually :
Press Add button
Netbeans 8.2 plugins portal
https://updates.netbeans.org/netbeans/updates/8.2/uc/final/distribution/catalog.xml.gz
If you use one of the latest openJDK (as you should), it doesn't provide unpack200 that will be requested to install C++ plugin.
You MUST have an older version of the openJDK installed (8, 11 or 13) to find them (or find the binaries and copy them on your system.
When you will restart Netbeans to install the C++ plugin, a Window will popup to say that it needs to find unpack200
For example you can find it here, on Ubuntu :
/usr/lib/jvm/java-1.11.0-openjdk-amd64/bin (symlink)
/usr/lib/jvm/java-11-openjdk-amd64/bin