Possibly Erichtites hieraclifolius (American burnweed)? Close up of leaves would help...

Ditto both comments.

I'm not convinced that the flower, which I agree looks like Erechtites, belongs to the bulk of those leaves, which appear compound, more like a Bidens.

Can you follow the flower stem down and verify if it is actually attached to those leaves? I'm pretty sure you'll find it is not and it is simply growing amongst another plant.

It is 100% neither Tansy nor Ragwort.

I will ask him to check those & take better pictures of the leaves - it is in his fenced back yard so I can't just mosey in hahaha.

I agree the leaves are compound. Thanks for the responses so far - please stay tuned!

He had started cutting them down, so these are photos of the lower stem. He said that for the first few months the stems are smooth, but become rather woody with the striations:

Hope this is sufficient for a good ID

So, the leaves are not compound.

Yes, those are the non-compound leaves of Erechtites hieracifolia. But they are not the same leaves as shown in the top photo which are very definitely compound and clearly belong to an entirely different plant.

I thought those were compound also. Thanks to all who answered and came up with the ID!

floraluk2, those were compound leaves! He finally confirmed that there were other plants besides the erechtites, and sent me a photo close up of the leaves