Hi @Adel Fattah ,
I am not sure where your mentor got this information from.
On the Microsoft Website is a clear statement regarding the region the Entra ADDS is installed in:
Two Windows Server domain controllers (DCs) are then deployed into your selected Azure region.
Source: How does Domain Services work?
This means the 2 VMs (DCs) of the Entra ADDS instance is installed in the selected region and if you select Switzerland North
the VMs will be deployed in this Azure region.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Andreas Baumgarten