The container documentation says that the layout setting is a string, as in the link below.
https://www.bryntum.com/docs/grid/api/Core/widget/Container#config-layout
But it can be a string or a layout configuration object. It would be interesting to change the documentation and the exported interface to Type Script, showing that it can be an object as well.
Something like this:
...
layout: string|object
...
