QTreeView can't hide columns & sorting question

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So, i've been trying to hide columns on a QTreeView before setting the QFileSystemModel, whatever, setColumnHidden() or header()->hideSection() doesn't work either, the column of the QFileSystemModel is still there.

And for sorting, i know there's a QSortFilterProxyModel, it's possible to for example put the folders at the end, and files with "x" extension at the start?
QSortFileProxyModel has a setFilterRegExp, so that works for the files with extension. But what about folders?
I think what i'm going to do here is more complicated. As, i want for example "x" extension always to be first, then "x" extension to be always second, etc.
I don't know if that's easily done.

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hideColumn() worked, but before didn't.