You can implement stackful coroutines yourself in C/C++, you need like 30 lines of assembly (as you can't switch stack pointers and save registers onto the stack from most languages). This is WAY better than what you could do for example with the way more convoluted C++ co_async/co_await for two reasons:
1. Your coroutine has an actual stack - you don't have to allocate a new "stack frame" on the heap for every "stack frame", e.g. every time you call a function and await it.
2. You don't need special syntax for awaiting - any function can just call your Yield() function, which just saves the registers onto the stack and jumps out of the coroutine.
Minicoro [1] is a single-file library that implement this in C. I have yet to dig into the Zig implementation - maybe it's better than the C++/Rust ones, but the fact they call it "async/await" doesn't bring me much hope.