> nor is there a simple way to target an older Glibc version without spinning up a docker container

? I feel like you might be falling into the trap of assuming that the compiler always targets the current running system, but you 100% should always always always be doing a Linux-to-Linux "cross" compile with a sysroot... you don't need a docker container: you just extract an old Linux distribution into a folder and tell your current/modern compiler to target it.