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.
{
    {
        const std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(m_node.chain.get(), "", CreateDummyWalletDatabase());
        wallet->SetupLegacyScriptPubKeyMan();
        wallet->SetMinVersion(FEATURE_LATEST);
        wallet->SetWalletFlag(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
        BOOST_CHECK(!wallet->TopUpKeyPool(1000));
        BOOST_CHECK(!wallet->GetNewDestination(OutputType::BECH32, ""));
    }
    {
        const std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(m_node.chain.get(), "", CreateDummyWalletDatabase());
        LOCK(wallet->cs_wallet);
        wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
        wallet->SetMinVersion(FEATURE_LATEST);
        wallet->SetWalletFlag(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
        BOOST_CHECK(!wallet->GetNewDestination(OutputType::BECH32, ""));
    }
}
static size_t CalculateNestedKeyhashInputSize(bool use_max_sig)