Not able to create relationships or create measures in SQL endpoint

Hi Anonymous ,
Thanks for using Fabric Community.
Apologies for the issue you have been facing. I tried to create a new relationship between two tables in my Lakehouse. There was no such error. I have attached the screenshots for your reference.

The error message you are getting indicates that the modeling service is unable to save your changes to the server because it references an object or property that is not available in the current edition of the server or the compatibility level of the database. This can happen for a few reasons:

• The server is running an older version of SQL Server than the client you are using to create the relationships or measures.
• The compatibility level of the database is lower than the version of SQL Server that the server is running.
• The object or property that you are referencing has been deprecated in the current version of SQL Server.

To fix this error, you need to identify the cause of the problem and take the appropriate action.

If the server is running an older version of SQL Server than the client, you need to upgrade the server to a newer version.

If the compatibility level of the database is lower than the version of SQL Server that the server is running, you need to upgrade the compatibility level of the database. To do this, you can use SQL Server Management Studio (SSMS).

Hence try creating the relationship between the tables after following the above steps.
If the issue still exists, this might require a deeper investigation from our engineering team about your workspace and the logic behind it to properly understand what might be happening. 

Please go ahead and raise a support ticket to reach our support team :

https://support.fabric.microsoft.com/support

After raising the ticket please share the details here as it would help us to track for more information.
Thank you.

Hope this helps. Please let us know if you have any further queries.