Sometimes products with sidebar menus need grids for specific frame sizes. It is convenient to use Stretch, but there is one nuance. Column sizes can become decimalized (because the original frame without the sidebar is not divisible by 12). This problem can be solved by compensating one of the sides with indents. In Figma unfortunately this functionality is not available, and should be added I think.
On the screenshot I drew a concept of how it could be
