Sorry, my mistake, it’s not in the form directly, but in the Transactions page. So if I create a new form and then receive a new “offline donation”, navigate to the transactions page, click “view donation details”, then change the status under “update payment” to complete, it doesn’t automatically apply the payment to the form in the all forms section.
But, if I get a new donation, go to the transactions page, tick the box for the donation and use bulk actions to “set to completed” then it will automatically add the funds to the form in the All Forms section.