Is there a way to group layers into a folder? I don't see an option for this anywhere.

Hhmm, I'm not really sure what you're asking. But maybe this info will help you. Inkscape's layers are apparently not set up like layers in other programs. Technically, Inkscape layers are special groups. So from that point of view, it certainly is possible to group groups. But as far as using the interface, i.e. Layers dialog, there's no visual way of doing that. Each layer stands alone.

However, Inkscape does offer sublayers. So for an existing layer, you could add (create) new layers as sublayers of that one. There might be some way to take existing layers, and make them into sublayers, by using XML Editor. But if there is, I couldn't telly you how.

I'll explain. In Photoshop, you can move multiple layers into a folder that appears in the layers box. This is very useful for keeping things tidy when you're working with many layers.

How do I create a layer as a sublayer?