"Legal action" lmao.
There isn't really much Singapore can do here,
it can't militarily force Indonesia,
Indonesia will laugh at any legal actions it brings to the world stage,
and if it tried a financial move it would just hurt its own reputation as a massive wealth laundering + tax evasion hub, Indonesia would even welcome that to be honest as it could then attract back hundreds of billions in wealth.
Singaporeans can oftentimes be delusional about their power and wealth, so they're seeing the real limits of it here.
JUST IN: Singapore's air quality reaches “very unhealthy” levels amid toxic haze from Indonesian forest fires, prompting officials to consider legal action.