In French there is a three-way distinction between (1) the ambiguous ‘végétarien’ (includes dairy and/or eggs??); (2) ‘végétalien’ (dietarily non-animalian); and (3) the quasi-religious ‘végan’ (which does not allow wearing leather, eating honey, killing cockroaches and so on).
In English, the empty semantic niche where French has (2) is filled either by the ambiguous ‘plant-based’ (but is 100% plant-derived food and, say, 70% plant-derived food not equally planet-‘based’?); or, by ‘vegan’, where this word is intended to apply solely to diet (minus the honey nonsense), and despite the unavoidably confusing association with the doctrines and practices of the aforementioned non-leather-wearing and non-cockroach-killing ethicalists.
In French, ‘plant oil’ is ‘huile végétale’; ‘végétale’ meaning ‘of or relating to plants’.
So as to fill in the missing semantic niche in English in a non-ambiguous way, I propose either or both of the following neologisms: (1) ‘plantarian’; (2) ‘vegetalian’.