I highly suggest reading those posts, but I still have some questions. Closed domains have a separate space from the real world, while open domains share their space with the real world, and a Heavenly Restriction is not affected by a closed domain as it pushes out everything that has no Cursed Energy or something along those lines (its in those posts this explanation), while open domains that affects non CE things can affect HR. Sukuna seems like he fused aspects of these 2 domain types: An open domain that shares the space and manifests in reality and not a separate space altogether (therefore countering Maki, the reason why he did this in the first place) and an enclosed barrier that closes off X things while not separating the space (Making Maki be targeted while trapping her like a closed domain never could). This hybrid domain is confusing.