Hi all,
thank you for your replies.

Replying to Palani:
We are not using the script tab since we are using simple conditions, as mentioned above.
In this case, we are distinguishing the priority of the tickets based on the "custom_field" we mentioned in the queues conditions (we are not using the "priority" ootb field). For example, if "custom_field" = 1 the queue has higher priority, while if "custom_field" = 2 the queue has lower priority.

Replying to Sulabh Garg:
We know that ideally we should have 1 queue = 1 assignment group, but the specific requirement in this case is in fact that we have 2 queues = 1 assignment group. These 2 queues should have a different priorty so that tickets belonging to Queue 1 (higher priorty) are assigned before to the operators.

Replying to Benoît:
Correct, this is the same goal we need to achieve.

For example: Operator 1 has a capacity of 10 tickets (10 tickets can be assigned to him) and we have 15 tickets created, 10 tickets associated to Queue 1 and 5 tickets associated to Queue 2. Even if the tickets associated to Queue 2 were created before than the tickets associated to Queue 1 (e.g. tickets for Queue 2 created on 21/02 vs. tickets for Queue 1 created on 22/02), the tickets associated to Queue 1 should be assigned earlier to the operator because Queue 1 has a higher priority.
It seems that the Order field is not suitable for achieving this goal.

Do you have any other suggestion?

Thank you all