finder "sort by" is greyed out when attaching a file to email

Toolbar, not Touchbar.

The window that opens when you click the Attach button is an Open File Dialog window.

Above what you posted should be a toolbar with buttons (tools) on it.

You should see one with four squares and one with lines. The squares chooses the View and the lines are the Group/sort button.

If you click on the Group/Sort button, you are choosing the grouping of the files. If you hold down the Option key on the keyboard while clicking, you can choose the sort.

You are in List View and have grouped them by Date. Click the Group/Sort button and choose None. Hold down the Option Key, click the Group/Sort button and choose your desired sort criteria. In List View, with no grouping, you can click on the column headers to sort.

Are you trying to sort the Open File dialog using Mail’s View menu, that won’t work. That is for sorting email messages. Use the Group/Sort button in the dialog Toolbar, just like you would in a Finder window.

To sort, hold down the Option key and click the button. Or, if in List View, just click on the column header.

I use them occasionally, but I do think the primary function on that button should be Sort, and the Option being Group.

I always think these things are Apple's passive aggression with new "features." They change historical behaviors to implement the new stuff that nobody asked for and they know nobody will use unless they make it unavoidable to stumble across.

The icons changed, but the open file dialog has been the same for several years.

As with the Finder, the Grouping options have been around for two to three years.