And which of these proprietary Clang forks have greater C++20 compatibility than free software Clang? The only proprietary fork of LLVM in the compatibility ta

And which of these proprietary Clang forks have greater C++20 compatibility than free software Clang? The only proprietary fork of LLVM in the compatibility table you linked is less C++20 compliant than free software Clang. So unless you have some causative explanation, I think the more sensible possibility is simply that the Clang developers have prioritized working on some of the plentiful other features of a compiler toolchain than perfecting their C++20 standards compliance. Blindly asserting (or implying) that if LLVM were GPLv3 then it would be more standards‐compliant, with nothing to back it up, doesn’t add much to the discussion, IMO.