Is it right time to invest in STI ETF as they involve a large portion of finance companies?

Long term investment, yes. Short time, unknown.

This is not the end of the pandemic yet. And theres a possibility of a further drop if unemployment get worst. (We are already in a recession now) For SG, we are lucky to have reserves to support us in this difficult times but if you look at other countries, the worst have yet to come.

And in Singapore, we do trades and businesses with people all over the world. If other countries are affected, we will get affected also.

Thus, best method now is to do regular DCA. Dont need to time the market. After 5 to 10 years you should be seeing positive returns.