https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97822
--- Comment #24 from LIU Hao <lh_mouse at 126 dot com> --- Dynamic stack realignment is not supported with SEH; there's no way to encode that information in SEH unwinding data. However: 1) MSVC access stack variables with unaligned instructions, and 2) Clang realigns RSP outside the prologue. (This is part of another issue: https://github.com/mingw-w64/mingw-w64/issues/115#issuecomment-3216258140)
