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 <wallet/coincontrol.h>
#include <wallet/context.h>
#include <wallet/receive.h>
#include <wallet/spend.h>
#include <wallet/test/util.h>
#include <wallet/test/wallet_test_fixture.h>
#include <boost/test/unit_test.hpp>
#include <univalue.h>
using node::MAX_BLOCKFILE_SIZE;
using node::UnlinkPrunedFiles;
namespace wallet {
RPCHelpMan importmulti();
RPCHelpMan dumpwallet();
RPCHelpMan importwallet();
static_assert(DEFAULT_TRANSACTION_MINFEE >= DEFAULT_MIN_RELAY_TX_FEE, "wallet minimum fee is smaller than default relay fee");
static_assert(WALLET_INCREMENTAL_RELAY_FEE >= DEFAULT_INCREMENTAL_RELAY_FEE, "wallet incremental fee is smaller than default incremental relay fee");
BOOST_FIXTURE_TEST_SUITE(wallet_tests, WalletTestingSetup)
static std::shared_ptr<CWallet> TestLoadWallet(WalletContext& context)
{
    DatabaseOptions options;
    options.create_flags = WALLET_FLAG_DESCRIPTORS;
    DatabaseStatus status;
    bilingual_str error;
    std::vector<bilingual_str> warnings;
    auto database = MakeWalletDatabase("", options, status, error);
    auto wallet = CWallet::Create(context, "", std::move(database), options.create_flags, error, warnings);
    NotifyWalletLoaded(context, wallet);
    return wallet;
}
static void TestUnloadWallet(std::shared_ptr<CWallet>&& wallet)