How do I invest in index funds (NOT ETFs), tracking indexes like the S&P500 or the MSCI World index in Singapore?

Cheap ETFs are (mostly) the better solution, also tradable during all opening hours of the exchange. cost reducing is so important.

my thinking:

https://seedly.sg/questions/what-is-your-genera...

The average index fund all-in expense is actually around 0.4 - 0.7% (Source: SPIVA) so I think its okay if you want an index fund at that expense ratio.

I would personally prefer index funds to ETFs because they force you to commit, lower tracking error amongst other benefits, even with a little bit more fees. Not easy to get though, as described below.