Okay, I can think of a ton of things that make this a stupid idea already.
There is no air gap and nowhere to put a heater.
2 and a half gallons is arguably too small for a betta to really thrive, let alone white clouds, danios, or goldfish.
There is no way a single betta fish could ever produce enough nitrogen to feed six actively growing herb or vegetable plants, which are very heavy root feeders. However, because these plants also have extremely high light requirements and this tank can not be set up near a window unless fried fish is desired, unless the tank is set under grow lights the plants will not survive long and then the water quality will deteriorate rapidly.
And even if the plants do survive, it will take at least 6 weeks of growth before they are large enough to sufficiently process all of the ammonia out of the water every day. The six weeks of ammonia buildup before then would surely kill any fish.
This could probably be used somehow with low-light, low-nutrient need plants like pothos, philodendron, syngonium, or peace lily, but would still be nothing more than a glorified fishbowl and would need to be treated as such.
I also see it mentions green beans as possibilities. Being legumes, beans actually pull nitrogen from the air and into the soil around them to survive. I can only imagine this would mean that beans in an aquarium would actually add even more nitrogen to the water column.