Two quite different things are called by this name and they need to be kept apart.
The first is a very large and very old class of marks: a circle with a cross inside it, a circle with spokes, a disc with rays. These occur on Bronze Age rock carvings in Scandinavia, on Iron Age Celtic coinage and votive wheels, on Slavic and Baltic textiles, in Christian ornament, and as pure decoration in dozens of unrelated settings. Some are securely solar. The Trundholm sun chariot, a gilded bronze disc drawn by a horse and deposited in a Danish bog in the second millennium BCE, is about as unambiguous as prehistoric evidence gets. Many other instances are called solar only because a wheel looks like the sun, which is a weak inference confidently repeated across a great deal of popular writing. The association of wheel, sun and turning year is genuinely present in Indo-European material, and it still does not license reading every circled cross as a sun.
The second is one specific design. The Sonnenrad, also called the black sun, is a twelve-rayed figure whose rays are shaped from the SS sig rune, set into the marble floor of the north tower of Wewelsburg castle in Westphalia, which Heinrich Himmler had converted for SS use in the late 1930s. It is a Nazi invention rather than a recovered antiquity. It was little known until neo-Nazi and esoteric-fascist writers took it up after the war, in part because it was not covered by the German prohibition on party symbols, and it has since become one of the most widely used identifiers of the international far right, appearing on the manifestos and equipment of several mass shooters.
The Anti-Defamation League lists that design in its hate symbol database and is explicit about the boundary: most sun wheel designs are unrelated to hate or white supremacy, while the specific Nazi-derived form is almost always used as a white supremacist symbol. That is the right way to hold both facts. A wheel cross on a Gotland picture stone, on a Latvian folk textile or in the head of a Celtic cross is not that design, and treating it as though it were concedes ground that does not need to be conceded.