This would allow wallet operations like funding transactions with smart contract-based inputs such as LN, or any input the Core wallet doesn't know how to sign for.

https://github.com/bitcoin/bitcoin/pull/17211#issuecomment-933674310
HelpExampleCli(method_name, "<txid>")
        },
        [want_psbt](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return NullUniValue;
    if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) && !want_psbt) {
        throw JSONRPCError(RPC_WALLET_ERROR, "bumpfee is not available with wallets that have private keys disabled. Use psbtbumpfee instead.");
    }
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VOBJ});
    uint256 hash(ParseHashV(request.params[0], "txid"));
    CCoinControl coin_control;
    coin_control.fAllowWatchOnly = pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
    
    coin_control.m_signal_bip125_rbf = true;
    if (!request.params[1].isNull()) {
        UniValue options = request.params[1];
        RPCTypeCheckObj(options,
            {
                {"confTarget", UniValueType(UniValue::VNUM)},
                {"conf_target", UniValueType(UniValue::VNUM)},
                {"fee_rate", UniValueType()}, 
                {"replaceable", UniValueType(UniValue::VBOOL)},
                {"estimate_mode", UniValueType(UniValue::VSTR)},
            },
            true, true);
        if (options.exists("confTarget") && options.exists("conf_target")) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "confTarget and conf_target options should not both be set. Use conf_target (confTarget is deprecated).");
        }
        auto conf_target = options.exists("confTarget") ? options["confTarget"] : options["conf_target"];