I never tried with TransferWise before... In this article I mentioned that I was using InstaReM instead.

In this scenario of transfer MYR to SGD then to USD, exchange fees hurt a little, but if you compare it to banks I think it's a lot cheaper if your amount if small (You might be able to negotiate with the banks for a better rate if your transferring a large sum).

You can always try different ways of funding your IBKR account and decide which is cheaper at the end of the day. Personally, this (InstaReM MYR to SGD to USD) is the cheapest route that is known to me so far. I'd love to know if there's another cheaper alternative.