A temporary drive is created by Azure compute platform for temporary storage. This is created for any VM created on Azure (VM creation experience below) not specific to ASR.
If you want to ensure windows volumes in Azure VM use the same drive letter assignment on-prem then you can run a simple command via Diskpart,
SAN Policy=OnLineAll
https://video2.skills-academy.com/en-us/azure/migrate/prepare-for-migration
There have been some enhancements recently and is set automatically for i.e. VMware agentless migrations.
Failed over VM’s will then retain the same drive letters and the temporary disk will use the next available drive letter.
----------------------------------------------------------------------------------------------------------------------
If the response helped, do "Accept Answer" and up-vote it