Add custom section to "Add new" menu

Dear Javier, 

You would need to add the record into EntityConnection table (you can do it with SQL executor or create lookup based on the object) with the  SysSchema.UId = EntityConnection.SysEntitySchemaUId for SysSchema.Name = Activity and EntityConnection.ColumnUId = SysEntitySchemaReference.ColumnUId for SysEntitySchemaReference with column name equals to your object. For implementing this please analyze the EntityConnection table and SysEntitySchemaReference  to have an understanding of which record you need to add. For example you can execute the following script: 

select SysSchema.Name, ColumnName, EntityConnection.* from EntityConnection inner join SysSchema on SysEntitySchemaUid = SysSchema.UId inner join SysEntitySchemaReference on EntityConnection.ColumnUId = SysEntitySchemaReference.ColumnUId

Best regards,

Dennis