I think it's a "snippet". Usually these are informative, or links to articles about online privacy, etc. Apparently now they're ads.
Ok, per https://twitter.com/asadotzler/status/1078366825736368128 it's an A/B test thing they've rolled out to some users in US for the holiday season.
No direct feedback channel, but they'll see our complaints or hurrahs on social media. :)
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