The biggest reason for a website traffic sudden drop is a latest Google update which impacted your website. The best reason to avoid this problem is regularly optimize your website with latest trends. The reasons can be following:

1. You have too much spam backlinks
2. You have duplicate, internal duplicate content on your website.
3. your content is written with AI tools, ChatGPT, etc.
4. Your website is not optimized with the keywords.
5. You have not fixed your website mobile-responsiveness & Core Web Vitals, These are some few factors you need to analyze to fix your website. There are many tools like SEMRush or AHREFs that can help you identify these factors.