Exchange2019-KB5074993

That SU is not publicly available. See Description of the security update for Microsoft Exchange Server 2019 CU15: February 10, 2026 (KB5074993) - Microsoft Support for information on how you can obtain it.  Basically, you'll need to sign up for ESU Period 2 (see Announcing Period 2 Exchange 2016/2019 Extended Security Update (ESU) program | Microsoft Community Hub) and then request the SU.