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{"gettxoutproof",
                "\nReturns a hex-encoded proof that \"txid\" was included in a block.\n"
                "\nNOTE: By default this function only works sometimes. This is when there is an\n"
                "unspent output in the utxo for this transaction. To make it always work,\n"
                "you need to maintain a transaction index, using the -txindex command line option or\n"
                "specify the block in which the transaction is included manually (by blockhash).\n",
                {
                    {"txids", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of txids to filter",
                        {
                            {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "A transaction hash"},
                        },
                        },
                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED_NAMED_ARG, "If specified, looks for txid in the block with this hash"},
                },
                RPCResult{
            "\"data\"           (string) A string that is a serialized, hex-encoded data for the proof.\n"
                },
                RPCExamples{""},
            }.Check(request);
    std::set<uint256> setTxids;
    uint256 oneTxid;