How to determine MAXDOP setting when using DTU in Azure SQL
DTU is a blended measure of CPU, memory, and data I/O and transaction log I/O…. This means that there is no definitive measure of equating x DTU = x CPU, X Memory etc.

Since, you have Premium P11 tier - this means that you have 1750 DTUs. Based on this blog post - By Andy Mallon, below is the CPU-to-DTU-to-Service Tier mapping :

+--------------+------+---------------+
| Number Cores | DTUs | Service Tier  |
+--------------+------+---------------+
| 1            |  100 | Standard – S3 |
| 2-4          |  500 | Premium – P4  |
| 5-8          | 1000 | Premium – P6  |
| 9-13         | 1750 | Premium – P11 |
| 14-16        | 4000 | Premium – P15 |
+--------------+------+---------------+

You should use Query Performance Insight for Azure SQL Database to review and adjust the db workload settings. Since you have db scoped configuration as non default (0 is default) - set to 1, you will need to review it and potentially change it so that you can utilize all the cores.