微软订阅修改用户登录时左上角的LOGO

https://admin.microsoft.com/Adminportal/Home#/Settings/OrganizationProfile/:/Settings/L1/CustomThemes

为你的组织自定义 Microsoft 365 主题
https://docs.microsoft.com/zh-CN/microsoft-365/admin/setup/customize-your-organization-theme

修改输入邮箱后显示的LOGO
https://docs.microsoft.com/zh-CN/microsoft-365/admin/setup/customize-sign-in-page