That is not a federal US law, depends on where in the US you live and probably mostly city or county level.

That's not generally true. In my current house, I own the land to the middle of the street. There is no sidewalk. The city has an implied easement (I've not found any documentation of it at least) covering the street and any drainage features abutting the street, although there are none on my side of the street. I can't place a sculpture on the road and expect it to remain, although there have been concrete blocks placed to obstruct parking since before I purchased the property, and they haven't been removed, so I could probably put some art there if I really wanted. Some of the lots around me do not extend into the street, and some do. As mentioned, sidewalks are not universal, and certainly not around here ... in town sidewalks are common, but lot boundaries are not consistent --- many lot lines on sidewalked streets don't extend into the sidewalk, but some extend into the sidewalk and the street surface. Regardless, art left on the sidewalk is likely to be removed, as it impairs access and the municipality has rights to maintain access to sidewalk regardless of ownership.

At my last house, I believe my lot went to the curb, although we never had it surveyed, and I didn't measure the width of the street. That wasn't in a city, but it did have a sidewalk; the county established standards for the sidewalk, but as the landowner, I was responsible for maintenance of it. The land between the sidewalk and the street was in my undisputed control, although looking at the county assessor interactive map, the lot line may fall a few feet on the house side of the sidewalk; the plat map shows a 50 foot gap in lots for the street and google maps measurement shows the street is much less than 50 feet.

Not necessarily. The sidewalk can still be owned but could be considered an easement, such that the owner can't restrict reasonable traffic flow along that easement.