Why does the Yoast Plugin show that your homepage is not indexable even though it is technically indexable or in the google index already?
This can have several reasons, the most common one is that the homepages URL differs. The plugin will take the WordPress 'permalink' of your homepage, but this must not necessarily be the factual URL of your homepage. For example even if your Server redirects all HTTP request to HTTPS, your Wordpress setting may still show an HTTP URL as Homepage. This is how you can check if your Homepage is indexable:
1. Copy your Hompage URL
Best to copy the URL right from the canonical tag.
2. Check it right with Ryte
The Single Page Analysis will give you a detailed overview of the URL, including indexability status. (Website Success Module)