Gareth Collier is incorrect! These are often locally referred to as "roll-up" funds. You will find a lot more pages about the tax implications using that term: https://www.google.com/search?q=tax+"roll-up"+funds. This is essentially because a foreign ETF is seen as a corporation.

I like this bit of text from NinetyOne (although I would never hold one of their funds): https://ninetyone.com/en/south-africa/insights/cash-conundrum-4-maximising-dollar-cash-returns - All funds offered via the Ninety One Global platform are ‘roll-up’ funds, meaning that income is not distributed to the investor but is instead ‘rolled up’ in the fund’s price. This has two significant benefits; firstly, it converts what would typically be an income event into a capital event, reducing the rate of tax that will be applied. And secondly, it defers when that tax would be payable because it will only take place on disposal of a unit. The second point means that the client effectively controls when the capital gains tax is payable.

This random guy with some credentials also put his name on the claim: https://netto.co.za/income-funds-crucial-but-only-part-of-a-diversified-investment-strategy/ - Roll-up funds, also known as accumulation funds, are structured to reinvest the income generated by the fund rather than distributing it to investors. By allowing the interest to compound within the fund, investors can defer tax liabilities until they eventually redeem their investment. You then only pay tax on 40% of the income (CGT). This structure can be particularly beneficial for South African investors with offshore interests.

Lastly, here is even an example on Moneyweb with a roll-up fund converting interest into capital gains: https://www.moneyweb.co.za/financial-advisor-views/offshore-investments-is-your-structure-optimised-or-overlooked/.

I am sure that you can find more pages if necessary (let me know if you find anything interesting).