Deprecation of SharePoint Add-Ins in Microsoft® SharePoint Online
SharePoint Add-Ins will stop working for new tenants as of November 1st, 2024 and they will stop working for existing tenants and will be fully retired as of April 2nd, 2026.
If you are using SharePoint provider hosted Add-Ins, it is recommended switching those applications to use Microsoft Entra ID for authorization and authentication needs.
References: SharePoint Add-In retirement.