Can use Wise to transfer money to Malaysian banks’ foreign currency accounts? Instead of letting the bank do the direct conversation at the respective bank rate.

Currently parking monthly FD, +/- 3% P.A not too bad...

I don't lose any conversion rates through banks. It's direct placement and transferable to Wise for conversion back to MYR if required. Also, waiting for final FOMC rates hike for 4.75% 12 months later on. 

But can you transfer from SG bank back to WISE? I read you can't receive money from outside Malaysia? Have you tried?

Of course you can but is silly to bring money back to Malaysia. One stuff I practice is one way ticket money and only bring it back if really needed. Or else, I won't bring back at all.