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.
for (auto entry : psbtx.unknown) {
        unknowns.pushKV(HexStr(entry.first), HexStr(entry.second));
    }
    result.pushKV("unknown", unknowns);
    
    CAmount total_in = 0;
    bool have_all_utxos = true;
    UniValue inputs(UniValue::VARR);
    for (unsigned int i = 0; i < psbtx.inputs.size(); ++i) {
        const PSBTInput& input = psbtx.inputs[i];
        UniValue in(UniValue::VOBJ);
        
        if (!input.witness_utxo.IsNull()) {
            const CTxOut& txout = input.witness_utxo;
            UniValue out(UniValue::VOBJ);
            out.pushKV("amount", ValueFromAmount(txout.nValue));
            total_in += txout.nValue;
            UniValue o(UniValue::VOBJ);
            ScriptToUniv(txout.scriptPubKey, o, true);
            out.pushKV("scriptPubKey", o);
            in.pushKV("witness_utxo", out);
        } else if (input.non_witness_utxo) {
            UniValue non_wit(UniValue::VOBJ);
            TxToUniv(*input.non_witness_utxo, uint256(), non_wit, false);
            in.pushKV("non_witness_utxo", non_wit);
            total_in += input.non_witness_utxo->vout[psbtx.tx->vin[i].prevout.n].nValue;
        } else {
            have_all_utxos = false;
        }