The native vlanVLAN is only relevant to 802.1q, yes it is untagged by default, but can be tagedtagged if required. Ports will be assigned to the native vlanVLAN if no other config is present.
ItsIt's ok to keep it as vlanVLAN 1, but it can be changed, you just have to remember to shut down unused ports, what i. What I mean by this, if iI plugged my evil hacker laptop into a working port that was left as vlanVLAN 1, iI could potentialitypotentially be able to span across your entire network, whereas you could change the native vlanVLAN to vlanVLAN 10, and then dontnot assign vlanVLAN 10 to any ports.
IslISL has no concept of a native vlanVLAN.