How to use layer folders in Fresco

What @Sjaani Said!. You can also click on the folder icon in the right bar, that will appear AFTER you've selected multiple layers.
To select multiple layers, either click on the 3 dots at the bottom of the right bar, choose "select multiple layers" and then click on all the layers you want selected in the layer stack, or even easier, click on the touch shortcut once to get the inner circle set in blue, and you'll be able to select multiple layers in the layer stack to group them.