I've never done that, but this is in the help file:

The backup is stored in the project tree in the "Name of the CPU > Online backups" folder. The backup is assigned the name of the CPU with the time and date of the backup.

Hello.

AutoGen_8008900

After doing Backup from online device, from an S7 1200 PLC, where is the backup file stored? I cannot find it anywhere on my hard drive.

Could you please be more specific on what you mean by "backup".

Some would understand "backup" as archive or even the offline project or (see PDF).

BR