What are the fees associated with TDAmeritrade if I want to buy ETFs? I know there’s zero commission fee, but are there any other fees such as fees for withdrawing money from the account?

I remember i had a $25usd withrawal charge from TD when i withdrew early this year.

There is a $25USD withdrawal charge

All the things there are:

https://www.tdameritrade.com.sg/why-td-ameritrade/pricing.html

for converting your SGD to USD to send to TD Ameritrade, let that currency switch do an independent, reliable service like TransferWise (or competitors), not your bank or broker who could charge 1.5 - 2.0 % conversion fees that are handled intransparently often​​​

Yes

Withdrawal requires u to wire to your bank account

Bank charges apply