It’s very difficult to get sufficient levels of B12 from whole food plant-based sources, which is why almost all doctors will recommend supplementation for vegans. While you could eat fortified foods with B12, it’s still hard to achieve a sufficient level of B12 because of the unpredictability of how much B12 the fortified food contains.
It’s also difficult to get D3 from vegan whole food sources, but you can get it if you get enough sunlight (roughly 20 minutes a day of direct sunlight), however, for those with pale skin, frequent prolonged sun exposure can also bring its own risks. Some 70% of the US population doesn't get enough vitamin D and vegans report especially low levels, as seen in the EPIC Oxford study.
Finally, some 64% of the general population were found to have suboptimal levels of the Omega-3 fatty acids EPA & DHA. Foods like flaxseeds and walnuts are a great source of the Omega-3 fatty acid ALA, which is then converted to EPA & DHA, but the process can be quite inefficient, which is why many doctors, like Dr. Michael Greger, recommend supplementing with an algae-derived source of Omega-3 (like ours). You can see his video here: https://nutritionfacts.org/video/should-vegans-take-dha-to-preserve-brain-function/
It’s also worth noting that both our D3 and Omega-3 are from plant-based sources (lichen and algae), however, as B12 is a form of bacteria, it's not possible to ascertain sufficient levels from a plant-based source.