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Sorry to hear that you were retrenched from your job.
Running a business from the comfort of your own home can be a practical choice, especially for those who are taking small steps to test the waters of entrepreneurship, or those who simply have limited capital and wish to save on operating costs.
The good news is that home businesses can in fact be run from HDB flats. However, all of HDB’s rules and regulations must be followed, and certain businesses are excluded.
The two government schemes concerning home businesses run in HDB flats are the Home Office Scheme and the Home-Based Small Scale Business Scheme. Here's a quick overview: https://www.propertyguru.com.sg/property-guides/hdb-home-office-and-home-based-business-guide-48790
Hope this answers your question.