Currently the feature for showing paintings on painting item tooltips is only applied to Items.PAINTING. If you instead checked instanceof HangingEntityItem and HangingEntityItem#type == EntityType.PAINTING it would allow the feature to work with mods such as Handcrafted - you can find their Fancy Painting implementation here. The caveat is that HangingEntityItem#type is private, so would need an Accessor mixin or equivalent.

holdup, are you sure they would have that type set to EntityType.PAINTING? wouldnt they have to useanother entity type?

well i see. added