Compound interest savings account vs index ETFs

Hello, I am a 21 year old and have around 18k that I get from the Korean military. I have an opportunity to put it in a annual 4.9% (variable interest) compound interest savings account for a max of 10 years. I am planning to also put in around $300 (max 15k) a month in this account for now until I have more income. There is no penalty for opting out at any point within the 10 years.

I also have around 6k in ETFs (VTI, AVUV, VXUS) and is wondering if its better since I am young to put the money in index ETFs. The weakening Korean currency kind of made me feel like I’m actively losing money by just having it in KRW, but then again compound interest is kinda hard to beat.

And advice would be appreciated.