To illustrate with a worked example: in SR1.5, the historical warming between 1850-1900 and the modern period of 2006-2015 was assessed as 0.87ºC, implying that the 1.5°℃ GWL would be accompanied by impacts associated with 0.63ºC warming from the modern period. However, AR6 WGI  revised the assessment of warming between 1850-1900 and 2006-2015 to 0.94℃, implying that the 1.5°C GWL would be accompanied by a slightly lower level of impacts associated with only 0.56℃ warming from the modern period. So, while the redefined 1.5°C GWL would be reached earlier, it would also be accompanied by a lower level of impacts . The impacts associated with the 'old' 1.5℃ GWL would now be seen at 1.57℃ global warming relative to 1850-1900, reached at the time of the 'old' 1.5°C GWL, if the same future level of warming were to be used as in SR1.5.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report