The flowers with serated leaves do look like a valariana. Is it definitely the smooth leaves that belong to it? You seem to have two plants mixed up there.
@REMF33 think the serrated leaves are the valeriana photos posted by silversurfer ( not the OP pics)?
edit to add - - although in the two leaf pics posted by OP ( the one where silver surfer could see the leaves were opposite in the first pic) - to me the second pic shows very slight serration.
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edit to add - - although in the two leaf pics posted by OP ( the one where silver surfer could see the leaves were opposite in the first pic) - to me the second pic shows very slight serration.
Don’t think the flowers are right for false lily of valley & the leaves of those are really smooth! But that’s the most like it so far.
The flowers are cream and frothy and not like the OP's photo. However, other forms of fagopyrum are available so maybe one of those would fit.