Another downside of using React App is that Google will crawl the site much less often and this can have a negative effect, as new content won't be crawled as often as a standard HTML and CSS website. Overall, React.js is not recommended for SEO in current times.
In summary, using Create React App without server-side rendering can have some negative effects on SEO. Other search engines, such as Bing and Yahoo, may not be able to crawl and index the content effectively, causing potential loss of traffic from these sources. Additionally, Google crawlers may crawl the site less frequently, resulting in slower indexing of new content.