The process is more involved than it seems at first, nasty toluene is required and only mentioned once in the methods section. The chemical treatment is a bit different, but I would expect similar results and difficulties as NileRed found when following the previous method from the same research group in 2016: https://onlinelibrary.wiley.com/doi/full/10.1002/adma.201600...

Also the drastic change of 1 mm thick balsa wood from rigid to foillike around 00:27-28 in the "Movie S2" of the supplemental material is quite surprising: https://advances.sciencemag.org/content/suppl/2021/01/25/7.5...