D3 is more effective in raising serum levels of vitamin D (87% more efficient according to [0]). However, D2 still helps and can be fine for people who aren't very deficient.
Also, there is D3 from non-animal sources. Although most D3 supplements are from lanolin (the fatty coating of sheep's wool), there are some plant-based D3. Most of the ones I've seen are derived from lichen (ex. [1]).
I mean the following more to elucidate than criticize.
A minor point of clarification (admittedly rather pedantic though in line with the many comments in this discussion which relate to scientific rigor) but the statements indicating lichen sourced D3 is plant-based can be misleading. While many lichens contain one or more algae species/strains (hence containing a plant) some do not. Some lichens contain cyanobacteria as their sole photosynthesizing member in symbiosis with fungi (ie. no plant involved.) I don't know the specifics of the lichen source for vitamin D3 production. So a plant may or may not be involved.
Based on vitamin D being produced by other fungi than lichens and no (known to me) plant source of D3 I'll venture a guess that the source of the D3 in lichens is from the fungal component. If this holds true then claiming lichen sourced D3 is plant-based is a bit of a stretch.
Of course a popular reading of "plant-based" as used in current diet marketing -which seems to mean anything not derived from an animal- could hold. But marketing speak is anything but scientific.
[Quick searches didn't lead me to clarity on whether algae are part of the lichens used for commercial D3 production. I do wonder why lichens were chosen over mushrooms. I'd have thought mushrooms would have multiple advantages.]
Also, there is D3 from non-animal sources. Although most D3 supplements are from lanolin (the fatty coating of sheep's wool), there are some plant-based D3. Most of the ones I've seen are derived from lichen (ex. [1]).
[0] https://academic.oup.com/jcem/article/96/3/E447/2597204
[1] https://www.amazon.com/Deva-Vegan-Vitamin-5000-Cholecalcifer...