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.
/** Calculate the size of the transaction using CoinControl to determine
 * whether to expect signature grinding when calculating the size of the input spend. */
TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control = nullptr);
TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const CCoinControl* coin_control = nullptr) EXCLUSIVE_LOCKS_REQUIRED(wallet->cs_wallet);
/**
 * COutputs available for spending, stored by OutputType.
 * This struct is really just a wrapper around OutputType vectors with a convenient
 * method for concatenating and returning all COutputs as one vector.
 *
 * Size(), Clear(), Erase(), Shuffle(), and Add() methods are implemented to
 * allow easy interaction with the struct.
 */
struct CoinsResult {
    std::map<OutputType, std::vector<COutput>> coins;
    
    std::vector<COutput> All() const;
    /** The following methods are provided so that CoinsResult can mimic a vector,
     * i.e., methods can work with individual OutputType vectors or on the entire object */
    size_t Size() const;
    
    size_t TypesCount() const { return coins.size(); }
    void Clear();
    void Erase(const std::unordered_set<COutPoint, SaltedOutpointHasher>& coins_to_remove);
    void Shuffle(FastRandomContext& rng_fast);
    void Add(OutputType type, const COutput& out);
    CAmount GetTotalAmount() { return total_amount; }
    std::optional<CAmount> GetEffectiveTotalAmount() {return total_effective_amount; }
private:
    
    CAmount total_amount{0};