Fruits and vegetables are less nutritious than they used to be

Yes and it’s less tasty too. GMO ruined it.

My understanding is actually that it was ruined by artificial fertilizer and monoculture, because those nutrients are drawn from the soil, and we only "feed" plants the nutrients required to grow and no other trace minerals. Eventually the soil becomes depleted and this causes them to be less nutritious.

Taste is affected similarly because we essentially chemically treat plants to make them take on more water and water them heavily to grow larger in size. Nearly every fruit and vegetable in the store is larger than it would be if left to grow wild, but they are more watery and less concentrated in flavor as well.

National Geographic is much less nutritious than it used to be as well.

This sparks an interest of mine. I want to grow my own garden of fruits and vegetables. I can grab seeds from my local hardware store. But are these genetically the best I can buy? Is there not a genetic strain of seeds that I can buy somewhere else, perhaps online, that produce both the most nutritious and delicious?

Yup this is exactly it. I don't think the issue is that our fruit is larger, but just that the soil is much more degraded. 90-95% of all plant species get the MAJORITY of their nutrients from mycorrhizal associations and some, like many orchids, are even obligate. Plant roots are generally primarily meant for communication and connection with fungi, not to extract nutrients from soil.

But when practicing monoculture, the #1 threat is pests and so we do everything we can to fight them. This includes using sterilized soils, an overreliance on pesticides, and the usage of artificial fertilizers. The artificial fertilizers are a particularly big problem when it comes to phosphorous because for most plants they rely on the depletion of locally available phosphorus before they start the complex chemical dance necessary to make the association with fungi

The really sad thing is that soil inoculated with fungi can hold 50-100x more water than sterilized soil. Without it water tends to drain and we use much more of it. Combine that with the fact that most of the phosphorus in artificial fertilizers is not actually accessible so we end up using more water which carries this leftover fertilizer which causes massive cyanobacterial/algal blooms that have already led to the extinction of many fish species.

It's a race to the bottom all to maintain the practice of monoculture. The research on mycorrhizae is relatively recent (mostly in the past 3 decades), but at this point the existing evidence is astoundingly clear. Plants with mycorrhizal associations better resist drought, frost, soil pathogens, produce more nutritious fruit, and can even produce more fruit mass (depending on the species, some will end up producing more leaves instead but this can be inverted with some manual labor)