I had a really bad fungus gnat infestation. I tried sticky traps, BT, and water with Fels Naptha soap. In the end, drying out the soil was the only thing that worked for me. I did it two different ways, but not sure if this is doable in your situation with veggies and planter boxes. For an avocado plant, I let the soil dry completely and then some before watering the plant again. The other was a money tree where I couldn't get the soil to dry fast enough, so I ended up repotting it with cactus mix. Once deprived of water, the fungus gnats disappeared.

Neem oil mixed with warm water and sprayed on the plants works pretty well.

Ladybirds (you can buy larvae which you can release in about 10 days) also works for aphids, they gobble them up.

Try: https://howmanyplants.com/post/bugging-out-tackling-common-h...