For climate attribution, the main challenge is the separation of externally human forced changes in the climate-related systems from their internal variability, while for impact attribution it often is the separation of the effects of other external forcings  from the impacts of the changes in the climate- related systems. Direct influences not related to changes in the climate- related systems could, for example, be pollution and land use changes amplifying biodiversity losses, intensification of fishing reducing fish stocks, and increasing protection reducing losses due to river floods. The direct human or natural influences may counter the impacts of climate change . Given the definition of impact attribution, this means that there may be an observed impact of climate change without the detection of a change in the natural, human or managed system. This is different from 'climate attribution', where detection and attribution usually are consecutive steps.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report