https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93821
--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> --- No, because that just makes it more awkward to write makefiles and build scripts. We used to do that, and it had no real benefit. If you want to use c++2a, you can use that. Other people just want to use c++20 across multiple releases, some of which have full C++20 support and some don't. To check the level of conformance you should check the macros defined by the compiler when compiling, not rely on which command-line options happen to be supported.
