Dear @h34rty
In your case, where the building is unsafe, old, and not in the depilated state, you can have these options.
You can file a complaint to respective municipalities or regional departments of the Real Estate Regulatory Authority of your state through the online grievance registration system of their official website.
Additionally, you can anonymously lodge a public grievance to nodal officers of respective housing departments or urban development departments through the online public grievance portal of your state government.
If your society has an active Resident Welfare Association (RWA), you can approach them with your concerns. They can often mediate or take up the issue on behalf of residents while maintaining anonymity.
In the online grievance, provide solid evidence to support your claims. This could include documents, photographs, videos, or testimonies from other residents. As you said, you can keep yourself anonymous by not revealing your name and other personal details to the public authorities.
The last option can be, to send a written grievance letter with supporting documents by post to the respective municipality or regional RERA office.