How many feet from fennel should vegetables be planted
All I can find is that vegetables should not be planted near fennel but nothing says how far apart.
Fennel is well known as an allelopathic plant. Here's an article that has more information on this quality: https://www.gardeningknowhow.com/garden-how-to/info/allelopathic-plants.htm
However, there's little research on this subject, especially on the distance that should be kept between the allelopaths and other plants. Since fennel roots are thought to produce chemicals which inhibit the growth of other plants, you'd want those the distance of their root spread, say 1 - 3', depending on the size of the plants. Some people have noticed that fennel seems to attract aphids, so if that's your worry, you might want to have a 10' separation. And if you're concerned about cross pollination with dill and coriander, the other side of the yard would be good.
Much of growing plants is experimentation. You could quarantine fennel away from the garden, but then plant a few different types of veggies near by to see what happens. Then let us all know.