No, it is not possible to register an Avanza or Nordnet account as the withdrawal account for your savings account with Nordiska.
Withdrawals can only be made to a pre-registered transaction account with a Swedish bank that is held in your own name.
The account must be a regular bank account, for example with SEB, Swedbank, Handelsbanken, Nordea, or another traditional Swedish bank.
Investment accounts with Avanza or Nordnet cannot be used for withdrawals, as they are not standard transaction accounts.