We study the static-quark entropy in QCD under external magnetic fields and use the temperature of its peak or equivalently, the inflection point of the renormalized static-quark free energy—as a pseudocritical deconfinement indicator. Calculations employ HISQ fermions with a tree-level improved Symanzik gauge action at physical quark masses, on lattices with $N_\tau$=8,12 and fixed aspect ratio $N_\sigma/N_\tau$=4. A two-dimensional $(T,eB)$ analysis yields $S_Q(T,eB)$, from which we extract $T_{pc}^{Q}(eB)$ and perform a continuum estimatation.
In the weak-field range explored, $T_{pc}^{Q}(eB)$ remains almost constant within error. We compare this deconfinement indicator with the total chiral susceptibility, finding comparable peak locations and a similarly weak $eB$ dependence within current uncertainties. These continuum results provide a controlled baseline for multi-observable studies of magnetic field effects on the QCD crossover at physical quark masses.