Hi, Sprout!
Because the none-default configuration is configured on the interface, the interface cannot be directly changed to access. By default, the interface is added to the vlan 1.
You need to run the port trunk allow-pass vlan 1 command on the interface to add vlan 1 and then change the link-type.
You can also run the clear configuration interface XX command to Clear the current configuration of the interface, and then reconfigure it.
Hope I can hope you!