“…The estimate (1.5) is comparable in strength to the Weyl bound for the Riemann zeta function and has long been regarded as a natural limit for the sup-norm problem in the squarefree level aspect [HT13,Remarks (i)]. It has been extended to number fields [BHM16,BHMM20,Ass24] and to more general vectors than newforms [HNS19,Ass21]. For levels that are not squarefree (e.g., powers of a fixed prime), the flavor of the problem is quite different (see Remark 1.4), and stronger estimates have been achieved in [Sah17,Mar16,Sah20,Com21,HS20].…”