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.
#include <string>
#include <utility>
#include <vector>
using interfaces::Chain;
using interfaces::FoundBlock;
using interfaces::Handler;
using interfaces::MakeSignalHandler;
using interfaces::Wallet;
using interfaces::WalletAddress;
using interfaces::WalletBalances;
using interfaces::WalletLoader;
using interfaces::WalletOrderForm;
using interfaces::WalletTx;
using interfaces::WalletTxOut;
using interfaces::WalletTxStatus;
using interfaces::WalletValueMap;
namespace wallet {
namespace {
WalletTx MakeWalletTx(CWallet& wallet, const CWalletTx& wtx)
{
    LOCK(wallet.cs_wallet);
    WalletTx result;
    result.tx = wtx.tx;
    result.txin_is_mine.reserve(wtx.tx->vin.size());
    for (const auto& txin : wtx.tx->vin) {
        result.txin_is_mine.emplace_back(InputIsMine(wallet, txin));
    }
    result.txout_is_mine.reserve(wtx.tx->vout.size());
    result.txout_address.reserve(wtx.tx->vout.size());
    result.txout_address_is_mine.reserve(wtx.tx->vout.size());