Microsoft have just advised in 365 Message center - Message ID MC1508562
Take action: NTLMv1 hardening changes might affect network connections on devices without Credential Guard
Beginning with the October 2026 security update, Windows 11, versions 26H2, 25H2, and 24H2, along with Windows Server 2025 enforce restrictions on generating NTLMv1-derived credentials for Single Sign-On by default. This planned security-hardening change is part of the boarder Microsoft effort to phase out NTLM. Microsoft originally documented the change in August 2025. This change applies only on devices with Credential Guard disabled, and might cause issues with Wi-Fi, Ethernet, and VPN connections that use MS-CHAPv2 authentication, resulting in possible failure to connect via Single Sign-On pathways...
It links to https://support.microsoft.com/help/5066470