Is it possible to group files and folders within a folder?

Think of it as being an 'open folder' I suppose. I select a group of files and folders and group them together.
So if you have multiple of these groups - you'd see them in the same lister view / pane, but they have separate view and sort options (just as though they were in their own folders, but are all visible together) ..

Is this possible in dopus?

If you want arbitrary sorting, Manual Sorting lets you drag things to any place you want them.

For arbitrary grouping, you could group by labels, comments/descriptions or even a script column to get custom grouping.

If you just need grouping and not sorting, using Flat View (Grouped) and placing the items in sub-folder is another option.