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{"combinerawtransaction",
                "\nCombine multiple partially signed transactions into one transaction.\n"
                "The combined transaction may be another partially signed transaction or a \n"
                "fully signed transaction.",
                {
                    {"txs", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of hex strings of partially signed transactions",
                        {
                            {"hexstring", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "A transaction hash"},