The XRP wallet has a minimum reserve requirement of 10 XRP coins. They are reserved when the account is opened and remain unavailable for withdrawal.
This is necessary to reduce the load on the ledger, prevent its excessive growth, and protect against spam. For example, if you top up an XRPL address with 30 XRP, 10 coins will be reserved for account creation, and the balance will show 20 XRP that can already be spent.
The minimum reserve requirement applies regardless of which non-custodial wallet is used for XRP.