> The Linux system API doesn't change much

really? they added epoll, aio (they later added io_uring as a better aio), ebpf. Real threads were added with clone(2). Routing changed from ipchains to iptables. They added all the stuff needed for containers: cgroups, namespaces and what else - the Linux system API saw lots of action.

Look here: lots of additions came since Linux 2.2 https://man7.org/linux/man-pages/man2/syscalls.2.html

They even added sysfs, as procfs is now regarded as 'old and cluttered'

Also lots of changes in glibc.