A GNU/Linux OS does not lack them. As do other OSes using Linux. Linux isn't a OS, it is a kernel. You wouldn't complain, that the NT kernel lacks a graphical file explorer.
Fair enough; the Linux kernel is arguably missing the API, but only for kTLS.
However, GNU/Linux does lack such an API. There is no standard API for listing certificates and private keys. All GNU/Linux provides is a list of files that may or may not contain one or more certificates and/or private keys that may or may not be related to each other. You have to go beyond the basic GNU parts to get to things like keychains.
