Fair question. I’m not an expert in EU law, obviously, but the answer seems to be that the Council of the EU, composed of the representatives of the national governments, have passed a series of directives which have placed specific individuals on the sanctions list. The various member states are then required to enact local laws to implement that sanctions list.
Here’s the most recent addition to the list of sanctioned individuals, as far as I can tell, adding a swack of Belerussian military officials to the list. Note that the new list starts at 697, so there are already 696 people on the list.
Here’s the rationale for putting number 697 on the list:
According to this French government article, the French are not confiscating assets of individuals on the sanctions list, but freezing them (“gel”). The owners can access them, in the case of physical things like boats, but can’t use them in any way or sell them.
I’ve not found a list of non-miltary types yet, so can’t comment on the rationale for putting them on the list.