You can have material that biodegrades, or material that doesn't biodegrade. But you can't have material that doesn't biodegrade that biodegrades. Plastic is a wonder material because it's a forever material.
You need to avoid certain kinds of biodegradation but you don't need "forever".
And in particular if you could make very small pieces biodegrade quickly, and only those, you'd instantly solve microplastics.
Not really relevant to geocells but quite relevant for e.g. timber, which might last a hundred years in a roof but start to rot in six months of composting.
Although that's not going to protect you from crystalline dust from silica and asbestos.