I cannot seem to get placement restriction working. All the other tweaks seem to be working for me except for this one. I'm playing on 1.16.5 and have everything fully updated.

Placement Restriction currently only works properly when the Fast Block Placement feature is enabled, as it was implemented for that feature initially. On its own it kind of has a one block offset it allows. It should get fixed when I have the time to rewrite all the placement related code.