https://safetravel.ica.gov.sg/arriving/general-travel/non-fully-vaccinated
It's unnecessarily complicated, and we all know why. In short:
1. You don't need to obtain permission to enter Sinkieland.
2. You need a pre-departure test 48 hours before boarding.
3. You will be issued a SHN on arrival for 7 days, and will receive your notice to for PCR test appointment. You will be released from your SHN at the end of the 7 days or negative result of your PCR, whichever is the later.
4. If you are symptomatic on arrival, you will be immediately tested.