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.
{
    
    CBlockIndex* oldTip = WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain().Tip());
    WITH_LOCK(::cs_main, m_node.chainman->m_blockman.GetBlockFileInfo(oldTip->GetBlockPos().nFile)->nSize = MAX_BLOCKFILE_SIZE);
    CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
    CBlockIndex* newTip = WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain().Tip());
    
    int file_number;
    {
        LOCK(cs_main);
        file_number = oldTip->GetBlockPos().nFile;
        Assert(m_node.chainman)->m_blockman.PruneOneBlockFile(file_number);
    }
    UnlinkPrunedFiles({file_number});
    
    
    
    {
        const std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(m_node.chain.get(), "", CreateDummyWalletDatabase());
        wallet->SetupLegacyScriptPubKeyMan();
        WITH_LOCK(wallet->cs_wallet, wallet->SetLastBlockProcessed(newTip->nHeight, newTip->GetBlockHash()));
        WalletContext context;
        context.args = &m_args;
        AddWallet(context, wallet);
        UniValue keys;
        keys.setArray();
        UniValue key;
        key.setObject();