The De Soto Plaza in in Coral Gables, FL, built in 1925, as seen at https://www.google.com/maps/@25.7450124,-80.275242,3a,75y,75... is not a modern roundabout. Granada Blvd does not indicate a yield-to-enter, while the others streets have stop signs.
I think that one should also have splitter islands.
(Video of its history at https://archive.org/details/Did_You_Know_-_DeSoto_Plaza_Foun... .)
I think Cocoplum Circle might count as a roundabout? https://www.google.com/maps/@25.7059315,-80.2608362,3a,75y,1...
There are also "traffic calming circles", which are not roundabouts. "Traffic calming circles should not be confused with roundabouts, which are designed to handle much higher traffic volumes and reduce vehicle delay." - https://www.sfbetterstreets.org/find-project-types/pedestria...