I use instarem to convert MYR to SGD then transfer to the IBKR Singapore account but it can be iffy sometimes, i have one (1) transaction missing / unmatched so far and it's a pain in the ass to get IBKR to solve it. After that I only use sg bank account to fund IBKR :/

It is best/safer to use your own singapore bank account and wire the money over. You can still use instarem or transferwise to wire money over to your own sg bank account, it's cheaper than using local bank's TT.