That place called Thomas Mews OX4 1BW

Other than the traffic islands, the London Place section only uses paint. There is no central vehicular barrier (will check).

"""
Roads are not to be mapped as dual carriageways if the two directions are only separated

* by paint. This includes single or multiple painted centre lines[1], hatched areas, channelized turn lanes[2], two-way turn lanes[2],
* by flush medians[3],
* or by any other means that is not a physical barrier to vehicles.
""" -- osm.wiki/Dual_carriageway

There may be a section it's reasonable to map as a short D.C. section to the NE of the Marston Rd traffic lights, but it's quite short. Is it worth it?

It's wide-sh, so an area:highway could be applicable for the micro shape mapping?

"Blemheim Road" doesn't exist, just a typo of Blenheim Road which already exists on OSM

closest bench is actually here (assuming bridge is at the right location)

This is Forest School

Roundabout layout changed. There is now a cut-through road across the roundabout. Traffic lights are missing as well

This roundabout has many more traffic signals than are currently mapped

via StreetComplete 38.2

This is confusingly mapped with separate trunk_link ways - given that there's no physical divider, it should be mapped as a single way but with lanes tagging (ideally by someone who, unlike me, understands lanes tagging)