I maintain backups using Time Machine and Carbon Copy Cloner, each on its own drive. The Time Machine drive is always connected. The CCC drive is disconnected most of the time. I do a CCC backup about once a week or before installing an OS update.
I do this for redundancy and to increase the chances of having a clean version of my entire setup in the event of a catastrophic failure or a security breach.
For backups, especially since macOS stopped supporting booting from clones some time ago, I use spinning platter HDs because I am not that concerned about I/O speeds, repeated reads and writes affect HDs less than SSDs, and the cost-per-megabyte is lower with HDs.