I get your point, but in this case it's not that we are pining for our favourite features from other languages, it's that even C++20 doesn't support any sensible style of error handling.

It just says "here are exceptions but also don't actually use them lol".

I'm paid to work on a vast C++ codebase which I am free to modernise but not to port. But when it comes to error handling there's not really anything to modernise to, so it's just this hige maintenance burden I can't fix.

...arguably you're better off using Rust anyway, if you have a choice.