Yoast has an incredibly feature-rich free version and is very easy to use for content creators. Focus-keywords, schema markup, meta title and description length

Yoast has an incredibly feature-rich free version and is very easy to use for content creators. Focus-keywords, schema markup, meta title and description lengths and so much more. They've also recently extended the plugin so you can access a post's metadata really easy when querying the WP REST API (or GraphQL API), this comes in handy when using WP as a headless CMS. I don't know of a comparable solution for React or Vue but I would be glad to hear about it.