Is this like a nested grid scenario i.e. Grid present inside another grid ?
If that is the case, then you can configure the parent grid with "Modal / Embedded pane" edit mode and inside the flow action, you can have the nested grid. This way you will be able to sort both the grids.
Nope, it is like - we are rendering a repeating grid based on a Page List and each element of the page list consists of an embedded page. And we want to sort the entire page list based on a property on that is present in that embaded page.