Duplicate/backup entire system hard drives

[cscs]

clonezilla would do it.
And a number of others … see this thread too:

How do I copy my Manjaro installation (and Windows) when replacing SSD to the new one?

This is correct. Whatever you read on reddit was either misinterpreted or plain wrong. What you probably want is something like disk cloning, such as dd or clonezilla or similar. https://wiki.archlinux.org/title/Disk_cloning