"The Fidelity debit card is available on youth accounts and nonretirement brokerage and cash management accounts with individual, joint tenant, and trust registrations"
If you withdraw money using a Fidelity debit card (without Financial Choice), from a brokerage account without any cash in it, that withdraw will create a margin loan that you have to manually pay back and that you also have to pay interest on.
If you withdraw money using a Financial Choice debit card, that withdraw will automatically trigger a sale of your stock in the appropriate amount, so that you won't be building up margin loans.
https://www.fidelity.com/cash-management/faqs-atm-debit-card
"The Fidelity debit card is available on youth accounts and nonretirement brokerage and cash management accounts with individual, joint tenant, and trust registrations"