You can check whether you are blacklisted by the Singapore Immigration by contacting the Immigration & Checkpoints Authority directly through their website, hotline, or email. One may contact a registered immigration agency about this or seek legal advice from an immigration lawyer. Common reasons that can get one blacklisted include overstaying, false information, criminal activities, and violation of visa conditions. In case you are blacklisted, it pays to know why and consider appealing, then strictly observe the immigration laws to correct your status.
https://www.oasis-india.com/how-to-check-if-youre-blacklisted-by-singapore-immigration/
