A user reported to me that they are unable to create a PSBT with a legacy watchonly wallet when they use the GUI. They get an error "The amount exceeds your balance".

I think the issue is that the GUI will retrieve the wallet's balance via `AvailableCoins` before calling `CreateTransaction`. This call to `AvailableCoins` is resulting in fewer coins being returned with recent changes to how `AvailableCoins` works, particularly with additional filtering of spendable coins and preset coins.

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Note that this does not effect descriptor wallets. A workaround for this issue is to switch to using descriptor wallets. An existing legacy wallet can be turned into a descriptor wallet using the `migratewallet` RPC. However many watchonly legacy wallets are likely the result of importing descriptors via `importmulti`. For such wallets, I recommend creating a new descriptor wallet and re-importing the descriptors.
const auto& res = m_wallet->createTransaction(vecSend, coinControl, !wallet().privateKeysDisabled(), nChangePosRet, nFeeRequired);
        newTx = res ? *res : nullptr;
        transaction.setTransactionFee(nFeeRequired);
        if (fSubtractFeeFromAmount && newTx)
            transaction.reassignAmounts(nChangePosRet);
        if(!newTx)
        {
            if(!fSubtractFeeFromAmount && (total + nFeeRequired) > nBalance)
            {
                return SendCoinsReturn(AmountWithFeeExceedsBalance);
            }
            Q_EMIT message(tr("Send Coins"), QString::fromStdString(util::ErrorString(res).translated),
                CClientUIInterface::MSG_ERROR);
            return TransactionCreationFailed;
        }
        
        
        
        if (nFeeRequired > m_wallet->getDefaultMaxTxFee()) {
            return AbsurdFee;
        }
    } catch (const std::runtime_error& err) {
        
        Q_EMIT message(tr("Send Coins"), QString::fromStdString(err.what()),
                       CClientUIInterface::MSG_ERROR);
        return TransactionCreationFailed;
    }
    return SendCoinsReturn(OK);
}
void WalletModel::sendCoins(WalletModelTransaction& transaction)