Perhaps it's Ageratina altissima.

Between the two you mention, it should be easy to tell apart. Comfrey has larger leaves, is fuzzy, but bristly and not soft. Buds are pink/lavender, opening to blue/purple. False gromwell has smaller leaves, I don't recall if they are fuzzy or not. Flowers are white/green and perhaps with a slight pink/lavender tinge. This is a wild prairie plant, and often grows with only one stalk.

That looks like impatiens balfourii, it just showed up in my garden this summer. It's kind of pretty and I've let it go to seed. Something tells me I'm going to regret this one, it looks very invasive. It is from asia.

They are excellent pollinator plants, blooming from early summer through the first hard Frost, providing a long season of nourishment. I would plant them where nothing else will grow, full sun and not much water if any. I've seen them growing on the west side of the house next to a heat radiating brick wall, I've seen them growing at gas stations where nothing ever gets watered, and I have my own little story. Several years ago, someone was to come dig some Mexican petunias for her own garden. It was so hot, and I wanted her little garden project to be a success, and I was afraid if she dug them up in the heat she would be too tired to plant them. So I dug them up for her lol. Put them in a wheelbarrow, spritzed them with water, and covered them up with a wet towel. She never showed up. So I took them to a hot, dry spot behind the garage, in full sun, where I had been thinking about making a compost pile.. I laid them on the ground, covered them with a little soil so I wouldn't have to watch them wilt & die, and said "rot in peace, amen". I now have a really nice, healthy little stand of them out there behind the garage, and they bloom their heads off all summer every year I put the compost pile somewhere else.