AFAIK, Gimp 2.99 introduced recently multi-layer selection, and since most scripts & plugins take an input layer, they know take a list of layers. So script/plugin registration changed somewhat to reflect this.
Python plugins need serious rework (migrate to Python3 and API changes), and the support of auto-generated parameter dialogs was incomplete last time I checked.
IMHO for regular work you are still better off with 2.10.