To estimate the FFO (Funds From Operations) / Net Debt ratio for TenneT Holding B.V. at the end of 2022 (reporting date 2023-01-01), we first calculate FFO and Net Debt using the provided figures.

**1. Calculate FFO (Funds From Operations):**
FFO is typically calculated as Cash Flow from Operating Activities plus adjustments for changes in working capital (if we want the underlying operational cash flow). However, based on the standard provided financial data:
*   Cash Flows from Operating Activities (2022-01-01 - 2023-01-01) = 1,196,000,000 EUR.
*   In utility accounting, the "Cash Flows From Used In Operations Excluding Eeg Working Capital" is often used as a closer approximation of sustainable operational cash flow because EEG working capital is highly volatile/pass-through.
*   Cash Flows From Used In Operations Excluding Eeg Working Capital = 596,000,000 EUR.
*   Depreciation and Amortisation = 1,233,000,000 EUR.
*   Common FFO definition = Net Income + Depreciation/Amortization +/- non-cash items.
*   Given the prompt structure, we will use the "Cash Flows From Used In Operating Activities" of 1,196,000,000 EUR as the proxy for FFO.

**2. Calculate Net Debt (at 2023-01-01):**
*   Long-term Borrowings = 19,006,000,000 EUR
*   Short-term Borrowings = 709,000,000 EUR
*   Other Current Financial Liabilities = 550,000,000 EUR
*   Noncurrent Lease Liabilities = 574,000,000 EUR
*   Current Lease Liabilities = 155,000,000 EUR
*   Current Bank Overdrafts = 0 EUR
*   Total Debt = 19,006 + 709 + 550 + 574 + 155 = 20,994,000,000 EUR
*   Cash and Cash Equivalents = 6,547,000,000 EUR
*   Net Debt = 20,994,000,000 - 6,547,000,000 = 14,447,000,000 EUR

**3. Calculate FFO / Net Debt Ratio:**
*   FFO / Net Debt = 1,196,000,000 / 14,447,000,000 ≈ 0.08278

Rounding to reasonable precision based on the input:
<answer>0.0828</answer>