I just used iNaturalist to finally the name of this stalwart perennial that’s been in my garden for years. I believe I purchased 1 plant for a deck container way back in 2008-ish. At some point I placed it in the garden next to a hosta which it became entwined with. I’ve divided said hosta several times and inadvertently transplanted this loosestrife along with it. It’s actually a much more awesome plant than the hosta (an unknown variety that was here when we purchased the house), and maybe this year I’ll see if I can divide it without the hosta roots!