When the newly introduced `"maxfeerate"` option is not passed, the default fee rate is interpreted as an absolute amount. However, when it is passed, it is interpreted as a fee rate. Thus, the rpc will return different results when the value is explicitly set to the default.

See

https://github.com/bitcoin/bitcoin/blob/536590f358dc3d3e5821eba7f1009452ea93b205/src/rpc/rawtransaction.cpp#L797-L807

I think we should change it back to an absolute value in BTC (not a feerate)

This was changed to a feerate by @kallewoof, so ping him to see if there was a specific reason to switch.
{
    RPCHelpMan{"sendrawtransaction",
                "\nSubmit a raw transaction (serialized, hex-encoded) to local node and network.\n"
                "\nNote that the transaction will be sent unconditionally to all peers, so using this\n"
                "for manual rebroadcast may degrade privacy by leaking the transaction's origin, as\n"
                "nodes will normally not rebroadcast non-wallet transactions already in their mempool.\n"
                "\nAlso see createrawtransaction and signrawtransactionwithkey calls.\n",
                {
                    {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The hex string of the raw transaction"},
                    {"maxfeerate", RPCArg::Type::AMOUNT,  FormatMoney(DEFAULT_MAX_RAW_TX_FEE_RATE.GetFeePerK()),
                        "Reject transactions whose fee rate is higher than the specified value, expressed in " + CURRENCY_UNIT +
                            "/kB.\nSet to 0 to accept any fee rate.\n"},
                },
                RPCResult{
            "\"hex\"             (string) The transaction hash in hex\n"
                },
                RPCExamples{
            "\nCreate a transaction\n"
            + HelpExampleCli("createrawtransaction", "\"[{\\\"txid\\\" : \\\"mytxid\\\",\\\"vout\\\":0}]\" \"{\\\"myaddress\\\":0.01}\"") +
            "Sign the transaction, and get back the hex\n"
            + HelpExampleCli("signrawtransactionwithwallet", "\"myhex\"") +
            "\nSend the transaction (signed hex)\n"
            + HelpExampleCli("sendrawtransaction", "\"signedhex\"") +
            "\nAs a JSON-RPC call\n"