For batch operations on GIMP 3, I've heard great things about Batcher: https://kamilburda.github.io/batcher/

Macros are on the roadmap (https://developer.gimp.org/core/roadmap/#macros-script-recor...), and in fact we did a lot of prepwork for them during 3.0's development (internally, several features like filters and plug-ins now have configs that store settings, which will be used by macros in the future to repeat operations).