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.
RPCExamples{
                    HelpExampleCli("getrawtransaction", "\"mytxid\"")
            + HelpExampleCli("getrawtransaction", "\"mytxid\" true")
            + HelpExampleRpc("getrawtransaction", "\"mytxid\", true")
            + HelpExampleCli("getrawtransaction", "\"mytxid\" false \"myblockhash\"")
            + HelpExampleCli("getrawtransaction", "\"mytxid\" true \"myblockhash\"")
                },
    }.Check(request);
    bool in_active_chain = true;
    uint256 hash = ParseHashV(request.params[0], "parameter 1");
    CBlockIndex* blockindex = nullptr;
    if (hash == Params().GenesisBlock().hashMerkleRoot) {
        
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "The genesis block coinbase is not considered an ordinary transaction and cannot be retrieved");
    }
    
    bool fVerbose = false;
    if (!request.params[1].isNull()) {
        fVerbose = request.params[1].isNum() ? (request.params[1].get_int() != 0) : request.params[1].get_bool();
    }
    if (!request.params[2].isNull()) {
        LOCK(cs_main);
        uint256 blockhash = ParseHashV(request.params[2], "parameter 3");
        blockindex = LookupBlockIndex(blockhash);
        if (!blockindex) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block hash not found");
        }
        in_active_chain = ::ChainActive().Contains(blockindex);
    }
    bool f_txindex_ready = false;