If I create an RBF transaction using the Qt GUI but specify my own custom change address, bumpfee doesn't work because it claims it can't find the change address:

    "Transaction does not have a change output"

This is because none of the outputs satisfy

    pWallet->IsChange(...)

I see there's a "TODO" commented in `CWallet::IsChange()` in `src/wallet/wallet.cpp`:

    // TODO: fix handling of 'change' outputs. The assumption is that any
    // payment to a script that is ours, but is not in the address book
    // is change.

I tend to put all my addresses in the address book whether I'm going to use them as change or not. I guess if the wallet was capable of creating its own SegWit change addresses I'd stop using custom change addresses, but currently it always seems to send change to a legacy address if I don't manually specify a change address.
{
    return RPCHelpMan{"walletprocesspsbt",
                "\nUpdate a PSBT with input information from our wallet and then sign inputs\n"
                "that we can sign for." +
        HELP_REQUIRING_PASSPHRASE,
                {
                    {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "The transaction base64 string"},
                    {"sign", RPCArg::Type::BOOL, RPCArg::Default{true}, "Also sign the transaction when updating (requires wallet to be unlocked)"},
                    {"sighashtype", RPCArg::Type::STR, RPCArg::Default{"DEFAULT for Taproot, ALL otherwise"}, "The signature hash type to sign with if not specified by the PSBT. Must be one of\n"
            "       \"DEFAULT\"\n"
            "       \"ALL\"\n"
            "       \"NONE\"\n"
            "       \"SINGLE\"\n"
            "       \"ALL|ANYONECANPAY\"\n"
            "       \"NONE|ANYONECANPAY\"\n"
            "       \"SINGLE|ANYONECANPAY\""},
                    {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
                    {"finalize", RPCArg::Type::BOOL, RPCArg::Default{true}, "Also finalize inputs if possible"},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR, "psbt", "The base64-encoded partially signed transaction"},
                        {RPCResult::Type::BOOL, "complete", "If the transaction has a complete set of signatures"},
                    }
                },
                RPCExamples{
                    HelpExampleCli("walletprocesspsbt", "\"psbt\"")