To determine the S&P credit trend for "A2A S.p.A." (and its subsidiaries) from 2021 to 2022, we apply the standard S&P methodology for calculating Adjusted EBITDA, Funds From Operations (FFO), and Adjusted Debt.

**Step 1: 2021 and 2022 Adjusted EBITDA**
A2A S.p.A.'s reported "Gross Operating Income EBITDA" provides a clean measure of operating performance, as the line item "Result From Nonrecurring Transactions" is reported below the operating profit and is thus already excluded. 
- **2021 Adjusted EBITDA:** €1,428 million
- **2022 Adjusted EBITDA:** €1,505 million

**Step 2: 2021 and 2022 FFO**
FFO is estimated by subtracting cash interest and cash taxes from Adjusted EBITDA. 
- **2021 FFO:** €1,428m (EBITDA) - €80m (Interest Paid) - €165m (Income Taxes Paid) = €1,183 million
- **2022 FFO:** €1,505m (EBITDA) - €75m (Interest Paid) - €201m (Income Taxes Paid) = €1,229 million

*(Note: Dividends paid were classified as operating activities by the company, but per S&P guidelines, we keep them strictly as financing outflows and do not deduct them from FFO).*

**Step 3: 2021 and 2022 Adjusted Debt**
We calculate Adjusted Debt by taking reported financial liabilities, adding pension deficits, and netting eligible cash. 
- **2021 Adjusted Debt:** €5,068m (Noncurrent + Current Financial Liabilities) + €294m (Pension Deficit) - €964m (Cash and Equivalents) = €4,398 million
- **2022 Adjusted Debt:** €6,889m (Noncurrent + Current Financial Liabilities) + €248m (Pension Deficit) - €2,584m (Cash and Equivalents) = €4,553 million

**Step 4: Ratios and Trend Analysis**
We can now calculate the leverage and coverage ratios to evaluate the credit trend:
- **2021 Leverage (Adjusted Debt / Adjusted EBITDA):** €4,398m / €1,428m = 3.08x
- **2022 Leverage (Adjusted Debt / Adjusted EBITDA):** €4,553m / €1,505m = 3.03x
  - *Change in Leverage:* -0.05x (A shift of less than 0.2x indicates a **Stable** trend).

- **2021 Coverage (FFO / Adjusted Debt):** €1,183m / €4,398m = 0.269 (26.9%)
- **2022 Coverage (FFO / Adjusted Debt):** €1,229m / €4,553m = 0.270 (27.0%)
  - *Change in Coverage:* +0.001 (+0.1 percentage points) (A shift between -0.03 and +0.03 indicates a **Stable** trend).

With both the leverage signal and the cash-flow coverage signal pointing to stability without substantial directional movement, the overall credit trend resolves cleanly to Stable.

<answer>Stable</answer>