Unless you’re targeting MSBuild Visual Studio Solutions and Windows only, C++17 is currently the most up to date, stable, and battle-proven version.
I work with C daily and I'm well aware of its many shortcomings (e.g. its huge list of undefined behavior and its PDP11-centric view of modern architectures), but with some effort I believe it could function as a semi-portable second-level intermediate representation. Nim uses it as such, IIRC.
Compiling to C first would introduce some of its own issues, for sure, but I imagine doing so would alleviate the pressure the C++ standards committee puts on compiler vendors each time they expand the size of the kitchen sink.
Which items from this table are lying about GCC v11 support of C++20? [1] Which of the features are buggy in GCC v11-12?
[1] https://en.cppreference.com/w/cpp/compiler_support#cpp20