I’ve recently setup a home server and since it’s equipped with a 1TB drive I also wanted to use it for backing up my iPhone.
On Big Sur, the iPhone can accessed directly via the Finder. You can configure and setup Wi-Fi sync via the finder.
As for the backups folder, the default path for saving the backups is:
We can’t change this path, but we can symlink it to another location. Make sure the Backup directory is empty or rename it to save your old backups. After deleting/renaming we need to create a symlink via the Terminal by executing the code below:
sudo ln -s /Volumes/backups ~/Library/Application\ Support/MobileSync/Backup
In my case
/Volumes/backups is a volume on the home server.
In case you get permission issues, make sure that your terminal has Full Disk Access enabled. You can enable this in System Preferences -> Security & Privacy -> Privacy -> Full Disk Access.
Reboot your computer and you’re good to go.