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.

***

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.
{
    if (new_balances.balanceChanged(m_cached_balances)) {
        m_cached_balances = new_balances;
        Q_EMIT balanceChanged(new_balances);
    }
}
interfaces::WalletBalances WalletModel::getCachedBalance() const
{
    return m_cached_balances;
}
void WalletModel::updateTransaction()
{
    
    fForceCheckBalanceChanged = true;
}
void WalletModel::updateAddressBook(const QString &address, const QString &label,
        bool isMine, const QString &purpose, int status)
{
    if(addressTableModel)
        addressTableModel->updateEntry(address, label, isMine, purpose, status);
}
void WalletModel::updateWatchOnlyFlag(bool fHaveWatchonly)