Just because it's in the name, doesn't mean it should be considered a fact or best practice in accordance with reality. I think this[0] reddit post frames it in the simplest way possible: "A backup is a copy of the information that is not attached to the system where the original information is."

There are many[1], many[2], many[3] articles about why "RAID is not a backup". If you google this phrase, many more people who are considerably more intelligent and wise than myself, can tell you why "RAID is not a backup" and it is a mantra that has saved myself, friends, colleagues and strangers alike a lot of pain.

[0] https://www.reddit.com/r/storage/comments/hflzkm/raid_is_not...

[1] https://www.raidisnotabackup.com/

[2] https://serverfault.com/questions/2888/why-is-raid-not-a-bac...

[3] https://www.diskinternals.com/raid-recovery/raid-is-not-back...

edit: formatting