Yes, backlinks are still relevant and continue to be an essential factor in SEO. They signal to search engines the authority, relevance, and trustworthiness of your website.
Link building itself is not illegal, but unethical practices such as buying links or engaging in link schemes violate search engine guidelines and can lead to penalties.
Link building can be both free and paid. Organic methods like guest posting and content marketing can be free, while paid methods include sponsored content or paid link placements.