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.
#ifndef BITCOIN_WALLET_SPEND_H
#define BITCOIN_WALLET_SPEND_H
#include <consensus/amount.h>
#include <policy/fees.h> 
#include <util/result.h>
#include <wallet/coinselection.h>
#include <wallet/transaction.h>
#include <wallet/wallet.h>
#include <optional>
namespace wallet {
/** Get the marginal bytes if spending the specified output from this transaction.
 * Use CoinControl to determine whether to expect signature grinding when calculating the size of the input spend. */
int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet, const CCoinControl* coin_control);
int CalculateMaximumSignedInputSize(const CTxOut& txout, const COutPoint outpoint, const SigningProvider* pwallet, bool can_grind_r, const CCoinControl* coin_control);
struct TxSize {
    int64_t vsize{-1};
    int64_t weight{-1};
};