Hello Rene, Laz,
Dynamic method to negotiate trunks is not recommended by Cisco. Cisco suggests manually configuring trunk links to avoid potential misconfigurations and security issues that can arise from automatic negotiation. I think this point should not be proposed in a lab like this and instead use manually configured trunk links. Best regards Michael.
Furthermore I am asking myself why spanning-tree is never applied to vlan 1. It’s normal business to set the priority higher then the others to prevent VLAN 1 becoming a root bridge.
spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1 priority 61440
spanning-tree vlan 1,10,20,30 priority 4096
spanning-tree vlan 10 hello-time 3
spanning-tree vlan 10 forward-time 10