Very tall (7 ft) plant, red stalks, long green leaves.

Could it be Japanese Knotweed? I suspect it is a weed.

 

IDK but I feel like we could figure it out with a few update pics. One showing the tips where the new growth is, and any blooms or buds that may have formed by now, and anything else you may have noticed about it since last posting.

Pokeweed seems unlikely from the standpoint that I've not heard of seedlings reaching such a size so quickly before, but it does look like it.

 

I very much doubt that it is japanese knotweed.