You can see WHT from your broker statement, and your Swiss ETF is indeed subject to 35% CH WHT.
| ETF / Stock | ETF / Stock domicile | WHT | Recoverable? |
|---|---|---|---|
| VANGUARD FTSE ALL-WORLD UCITS ETF | IE | - | - |
| ISHARES CORE SPI ETF (CH) | CH | 35% in CH | By filling your tax declaration in CH |
| ISHARES CORE MSCI WORLD UCITS ETF USD | IE | - | - |
| AMD | US | 15% in US | Through DA-1 |
| Apple | US | 15% in US | Through DA-1 |
| Qualcomm | US | 15% in US | Through DA-1 |
It looks like your US stocks are the only ones relevant for DA-1, and the tax authorities will process your DA-1 only if your are claiming at least 100 CHF of recoverable WHT. If you haven’t reached the threshold you can select “Revenus non soumis à l’impôt anticipé et non soumis à l’impôt étranger retenu à la source” when you enter your US stocks positions (but you still need to enter your gross dividend incomes, i.e., before WHT which is unfortunately lost) and you enter your net dividend income (gross income minus WHT) in the “Revenus bruts en CHF” field.