Is it possible to create a custom approval workflow for EFT payment batches? By using a workflow or script (not the approval routing tab on the company bank detail record)

I believe, yes. You probably cannot replace the native EP routing without the bank detail approval tab, but you can enforce your own workflow or script on the Payment Batch that requires a custom "Approved for EFT" flag before users can generate the file. With the right role permissions, that gives you a clean approval layer outside the standard routing.

I would say yes but you have 2 options. Use NetSuite or banks have an approval process usually that can be used. We usually rely on the bank ones before the funds get release and each of our bank accounts can be selective based on their criteria.

By the way, we're using the Payments > Payments Processing> Payment Batch List path. We generate a payment batch that is based off a saved search. This payment batch seems to be a suiteñet when using the native approval routing. So I don't understand how we would be able to override this approval logic.