You can simply copy the wallet.dat file to an encrypted USB drive or a secure cloud storage service (though cloud storage is generally discouraged for high-value keys).

wallet.dat is the default wallet file for Bitcoin Core (formerly Bitcoin-Qt). Unlike lightweight or web wallets that outsource key management, Bitcoin Core stores everything locally. The file is an (since v22.0) or a Berkeley DB (BDB) file in older versions.

At its core, wallet.dat is a Berkeley DB (BDB) file, though newer versions of Bitcoin Core have transitioned to a SQLite-based format for improved reliability. The file serves as a deterministic key-value store, but its contents are hierarchically profound. It contains a pool of private keys (often 100 pre-generated keys by default), their corresponding public addresses, transaction metadata, and crucial chain state data.

"Process Memory Investigation of the Bitcoin Clients Electrum and Bitcoin Core" demonstrates that wallet.dat

A collection of pre-generated keys for future use.