Maintenance mode in D365 FO LCS

 https://learn.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/sysadmin/maintenance-mode

https://daxonline.org/1913-enable-disable-d365-maintenance-mode.html

Enable in Dev tier-1 environment 

https://community.dynamics.com/blogs/post/?postid=de23b7f7-9444-42ef-beb8-1ac4c28ccf69

https://www.cloudfronts.com/blog/dynamics-ax/how-to-enable-disable-maintenance-mode-using-sql-query-in-dynamics-365-for-finance-operations/

Enabling and disabling maintenance mode in Dynamics 365 Finance and Operations (D365 FO) through Lifecycle Services (LCS) is essential for making system-wide changes. Here’s how you can do it:

Enabling Maintenance Mode

1. Navigate to Environment Details:
• Go to the Environment details page for your desired environment in LCS.
2. Enable Maintenance Mode:
• Click on Maintain > Enable Maintenance Mode.
• In the slider, set Turn maintenance mode on for the environment and select Confirm¹.
3. System in Maintenance:
• A servicing operation begins, and your system goes into maintenance mode. The environment state will change to In Maintenance¹.
• Only system administrators and users with the Maintenance mode user role can sign in during this period¹.

Disabling Maintenance Mode

1. Disable Maintenance Mode:
• Once your changes are complete, go back to the Environment details page.
• Click on Maintain > Disable Maintenance Mode¹.
2. System Back to Normal:
• A servicing operation starts to take your environment out of maintenance mode. The environment state will revert to Deployed, and all users can sign in again¹.