Use a shared folder with Time Machine
You can use a shared folder as a Time Machine backup destination.
Set up a shared Time Machine backup folder
Choose Apple menu > System Preferences, then click Sharing.
Select the File Sharing checkbox.
Click the Add button at the bottom of the Shared Folders list.
Navigate to and select the folder you want to use for sharing, then click Add.
Select the name of the shared folder, click Options, then make sure “Share files and folders using SMB” is selected and “Share files and folders using AFP” is not selected.
Control-click the name of the folder, then choose Advanced Options.
Select “Share as a Time Machine backup destination.”
If desired, select “Limit backups to,” then enter a size.