We establish a cosmological-model-independent method to extract the apparent magnitude and its derivative at different redshifts from the $\mathrm{Pantheon}+$ type Ia supernova sample and find that the obtained values deviate clearly from the prediction of the $\mathrm{\Lambda }\mathrm{CDM}$ model at the lowest redshift. This deviation can be explained as a result of a transition of the absolute magnitude $M$ in the low-redshift region. The observations seem to favor this transition, since the minimum values of ${\chi }^2$ for two Ansätze of a varying $M$ are less than that of a constant $M$. The Hubble-constant tension is alleviated from larger than $5\sigma$ to be about $1\sigma –2\sigma$ for a varying $M$, and the growth tension can be resolved after attributing the variation of $M$ to a modification of the effective Newton’s constant.

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• Cosmological parameters