Based on the information on the fee schedule page shared above, Gemini does not charge any withdrawal fees except for the network fees. However, the fee rate they charge might be a bit higher than what some fee estimators like mempool.space might suggest to ensure the transaction gets confirmed quickly even in case of a sudden spike in network congestion.
Through payment batching, they pay much lower fees than the user pays for their transaction, and with the low confirmation fees for most blockchains, withdrawal fees generate good profits for them.