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.
view.SetBackend(viewMempool); 
        for (const CTxIn& txin : psbtx.tx->vin) {
            view.AccessCoin(txin.prevout); 
        }
        view.SetBackend(viewDummy); 
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vin.size(); ++i) {
        PSBTInput& input = psbtx.inputs.at(i);
        if (input.non_witness_utxo || !input.witness_utxo.IsNull()) {
            continue;
        }
        const Coin& coin = view.AccessCoin(psbtx.tx->vin[i].prevout);
        if (IsSegWitOutput(provider, coin.out.scriptPubKey)) {
            input.witness_utxo = coin.out;
        }
        
        
        
        SignPSBTInput(public_provider, psbtx, i,  1);
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
        UpdatePSBTOutput(public_provider, psbtx, i);
    }
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    return EncodeBase64((unsigned char*)ssTx.data(), ssTx.size());
}
UniValue joinpsbts(const JSONRPCRequest& request)