The Linux kernel itself is GPL, and the GPL protocol itself is copyrighted rather than copyright-free.
For example, all Android phones and tablets are based on the copyright rules of the GPL protocol itself and must be implemented according to the GPL protocol rules. In other words, the kernel source code must be provided to users. But apart from the kernel, Android is APL, but it doesn't need to provide source code (but it needs to explain the patent right). Therefore, at present, domestic tablet computers are basically copyrighted, because the GPL protocol has not been fulfilled.
But if your system is mixed with other LGPL, GPL or other source code and function libraries. Then your system should consider the problem of "GPL infection". Relatively speaking, the kernel only infects the driver module. Programs running on the Linux kernel are not affected by GPL.
The Linux kernel of GPL is copyrighted, and the additional requirement of copyright is that you must abide by GPL when using it. GPL protocol can only be realized based on copyright ownership.
But then again, isn't it a bit "redundant" to discuss copyright issues in China?