Why is this program erroneously rejected by three C++ compilers?

C source code reducer

A header-only, conservative tracing garbage collector in C

PCB devboard the size of a USB-C plug

Lisp-style C++ template meta programming

M.C. Escher Flavoured Pages

I used C++ and nanobind to build a zero-copy graph engine that lets Python train on 50GB datasets

NumenText: a non-modal terminal IDE with LSP and DAP, inspired by Borland C++

A header-only C++ library for the TOON configuration format

Should I learn C and or C++ before learning go and why?