If I have 30k worth of savings for marriage and I'm planning to get married in the next 3 to 4 years. Should I be investing that money or keep it in a bank?

Option: safest to risky

1) Fix deposit (1%+)
2) high yield account eg. Dbs multiplier- 3.8% max (T&C)
3) Money market fund (0.x%)
4) bond UT (3%+ p.a.) monthly dividend (very stagnent). Eg pimco fixed income.
5) equity fund (3%+ p.a.) monthly dividend (some growth). Eg. UOB global quality fund

If only $30k wont suggest ETF, if you only willing loss $2000. There is a potential to grow higher but if there is a correction portfolio can down 30%.

With very low risk investment, typical return is 3%+. So around $3.6k+ after 4 yrs. Is it acceptable?

$2,000 / $30,000 is approx 6.67%. Given your short investment horizon and conservative risk appetite, you can invest in portfolios with a greater proportion of fixed income assets and a lower proportion of equities. However, if you plan to invest through a robo-advisor, you need to take into account the platform's fees. Fees are charged throughout the period your money is invested, regardless of profitability.

If I were you, I will keep this money in cash management or insurance savings.​​​