What not to plant together in a container raised garden???
Are tomatoes okay next to potatoes and peppers ???...
Unfortunately, companion planting has not withstood the test of scientific studies. That said, giving a plant adequate spacing for root growth and to prevent shading of adjacent plants is important.
Some recommend planting top-growth plants like tomatoes next to tuberous veggies like potatoes, carrots and beets. If you are hoping to plant your veggies close together, look up Square Foot Gardening. I found a webpage that has good info on this approach. https://www.ag.ndsu.edu/publications/lawns-gardens-trees/the-facts-of-square-foot-gardening
These articles will help you.