This is not true. IE11 simply doesn't support the whole of CSS Grid, and tools like Autoprefixer don't and can't add support.
If you limit yourself to only using the parts of CSS Grid that IE11 supports, then you can write the standard equivalent to that subset and Autoprefixer will translate it for you, but you can't "just write standard grid layout", because that includes things there is no IE11 equivalent for.
If you limit yourself to only using the parts of CSS Grid that IE11 supports, then you can write the standard equivalent to that subset and Autoprefixer will translate it for you, but you can't "just write standard grid layout", because that includes things there is no IE11 equivalent for.