There’s 15-30% withholding tax from the US whenever a payment cross its border: dividend payment from a US stock to non-US shareholder (e.g. you or the Irish fund), or a distribution payment from US fund to non-US shareholder (you). Dividend from US stocks to US funds isn’t taxed.
You can recover this tax only on a payment to you, if you owe taxes on it in Switzerland. US-CH have income tax treaty, income is not supposed to be double taxed, hence CH will reimburse or write off the non-reclaimable US tax on your CH taxes. But if withholding was done on a payment to the non-US fund, it’s the fund that gets hit here and there’s nothing you can do about it, but take the loss
The situation seem to be similar with many other countries: most countries withhold some non-reclaimable percentage of dividends and you’d only get compensated if you’re a direct shareholder and income tax treaty allows it. If you want to invest in a single world-covering fund, then optimize for US as it’s the biggest elephant in the room, and so I’d go for VT out of your two choices
Only for US stocks/funds and only if using a swiss broker. So just don’t use swiss brokers and this problem is solved.
Most stocks pay dividends, so it’s pretty hard to avoid them and taxes in a normal fund. But there are non-dividend payment companies that work a lot like investment funds. Berkshire for example.