There is no magic number but most new blogs start seeing consistent traction somewhere between thirty and fifty well researched articles, the early posts often go unnoticed because search engines need time to crawl, index, and understand your site's authority, each new piece of content adds another potential entry point for visitors and gives you more data about what your audience actually wants to read.
What matters more than the count is the quality and strategy behind those posts, a blog with twenty exceptional pillar articles that thoroughly cover core topics will outperform a blog with one hundred shallow posts, search engines reward depth and topical authority, if you publish consistently over three to six months while building internal links between related articles, you start to create a structure that google recognizes as a real resource in your niche.