Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi there,
This is new sign in Office 365 experience, you will not get option to ticked "Keep me signed in" on the login page.
You can directly reported here https://techcommunity.microsoft.com/t5/Office-365/New-sign-in-experience-for-Office-365-what-s-it-about/td-p/91913/highlight/false
Thanks,