We're unlikely to see F return before an effective vaccine is widely available, in my opinion. I wouldn't even like to speculate when that'll be.
SQ's First class service has a lot of passenger-staff interactions, elaborate meals - all of which aren't possible under the current health rules. Until those rules are lifted I don't imagine SQ would attempt to resume F even if there was enough passengers to make running an A380 or B777 - who is going to pay all that money for a pre-wrapped tray meal and no drinks service? (Take a look at
https://mainlymiles.com/2020/09/24/s...ional-flights/ which outlines the scenarios in which normal cabin service could be permitted. The only countries with low enough COVID cases to be classified as low risk aren't accepting travellers.)