Would you recommend investing with a robo-advisor or investing into ETFs for a beginner? Why?

TBH, why not do both? Robos don't exactly offer you the exact ETF you are looking for, and more often than not, they have their own constructed asset allocation which may or may not be what you're looking for. However, you can see robo as the professional segment of your investments. And then DIY and buy ETFs of your choice, but make sure you don't overlap if not you are being redundant. For myself, I have my own DIY portfolio as well as a Robo segment. Hope it helps!

I believe that both strategies are the same in the sense that they use the same financial product which is ETF. I would recommend investing with a robo-advisor because for beginners, they may not know what ETFs to buy. Should I buy STI ETF or S&P500 ETF or World Stock ETF or which sector ETF to get the most gains etc. With robo-advisor, they will properly allocate those ETFs that has potential because there's always one professional behind this robo-advisor running those algorithms.

So if you know what ETF to buy, I would recommend doing DIY ETF RSP through FSMOne's ETF RSP or IBKR (for ireland domiciled etf).

However, please bear in mind that you might incur more costs if you want to buy a lot of ETFs compared to robo advisor where they charge you by AUMs. Therefore, to me, I would choose a World Stock ETF to invest in so that almost all aspects of the stocks are covered in one ETF and thus saving cost.