Both are European-focused cards, but they sit on opposite sides of the custody line — the single most important difference here. The Nexo Card is custodial and can borrow against your collateral in credit mode, with the liquidation risk that implies.
Gnosis Pay is self-custodial: your funds stay in a Safe smart wallet you control, and the card spends straight from it on-chain. That appeals to people who do not want a company holding their balance, and its cashback is tiered to GNO holdings. It is very much an EU-first product.
Want to keep custody of your own funds and are comfortable with a smart-wallet setup? Gnosis Pay is the reason to look. Prefer a managed card and maybe a credit line against your crypto? Nexo fits that. Fees we have not verified ourselves are labelled unconfirmed.