Is it still not possible to use EFT for Vendor Prepayments?

not until 2021.1

It's possible if you use the discontinued NetSuite bundle for prepayments. You'd have to open a case within NetSuite requesting that and explaining that you want to use EFT for Vendor Prepayments. The current feature does not support the EFT functionality yet.

Thanks everyone! Will have to wait until May then.