No, SEO (Search Engine Optimization) cannot be done without a website. SEO is the practice of optimizing a website to increase its visibility and ranking in search engine results pages (SERPs).
In order to optimize a website for search engines, you need to have a website to work with. SEO involves various techniques such as keyword research, on-page optimization, link building, and content creation, all of which are done on a website.
While there are some off-page SEO strategies that can be implemented without a website, such as creating social media profiles and building backlinks from other websites, these techniques are typically more effective when used in conjunction with on-page optimization.
So, to sum it up, having a website is a prerequisite for doing SEO.