Please see Travel Advisories from the Singapore’s Ministry of Health (MOH) on COVID-19 :
UPDATE FROM 10 JULY 2021, Given the worsening situation in Indonesia, we will tighten our border measures for passengers from Indonesia by reducing entry approvals for non-Singapore Citizens/ Permanent Residents with immediate effect. Entry approvals may be considered where additional safe management measures are taken.
WITH EFFECT FROM 12 July 2021, 2359 hours , Passengers with travel history to Indonesia within the last 21 days will not be allowed to transit through Singapore.
Passengers entering Singapore with recent travel history to Indonesia within the last 21 days prior to departure for Singapore will be required to present valid negative COVID-19 PCR test taken within 48 hours before departure for Singapore.
For more info: https://safetravel.ica.gov.sg/
Tracetogether for visitors in Singapore
Click here for more info : https://www.brf.com.sg/tracetogether-for-visitors-in-singapore/