Cool! I actually helped add Amiga ILBM support to #GIMP in the development version: https://www.gimp.org/news/2023/07/09/gimp-2-99-16-released/#new-image-format-supports-pam-qoi-amiga-iffilbm-dcx
We're in feature freeze as we get ready to release 3.0, but after that I plan on adding more features to our Amiga plug-in. I'd also be interested in adding support for the brush format if you could share some sample files (the issue tracker is here: https://gitlab.gnome.org/GNOME/gimp/-/issues/6161)