Hello folks!
I've found a little conflicting information on this - historically there have been mentions of people having to provide copies of UK naturalisation certificates, statements they're not relinquishing US citizenship and so on. However, looking at the DS-82 (DS-82 04-2022) which the US Embassy suggests to fill out, there's no mention of anything like this, just a routine renewal form.
Have I missed something rather obvious, or is it now streamlined and the US State Department doesn't need that detail any more?