What are we looking at? Motionblur in Post with motion vectors or directly rendered in Cycles?
Directly rendered in Cycles.
The setting is hidden inside the object properties (only when cycles is selected)
unfortunately motion blur does not work for lights and several other objects (while it works in eevee as it basically renders the scene over and over)
Looks like you are using a very slow shutter speed (high shutter value in cycles) to achieve the smearing effect. Probably needs a lot more Steps (in the object motionblur settings) to get a propper result.
@ Atair & Habauk, OMG, thank you so much, that fixes it! (put “steps” to 7)