I don't know much about Zig, but it shares a problem with Rust in that neither have a built-in REPL.

I'd like to learn Rust, but every time I try to, I am a bit overwhelmed by its complexity, both in syntax and overall feature set.

The evcxr project https://github.com/google/evcxr is implementing what amounts to an experimental Rust REPL. (Though there's inherently something a bit weird about a REPL for C/C++-like languages, where the phase separation between compile- and run-time is so inherent to the programming model.)