NetworkManager is a software utility for configuring and managing network interfaces. It is developed by the Gnome project and is used in many distributions and by many Desktop Environments. The stated goal of NetworkManager is to make setting up and configuring networking as automatic and painless as possible, so that it just works. To aid in this goal NetworkManager can perform connectivity checking in order to determine whether your network has full internet connectivity.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-prevent-networkmanager-connectivity-checking