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This Post is similar to another one with in-depth responses so give this a quick read through.
https://answers.netlify.com/t/can-i-move-my-wordpress-to-netlify/4411
TL:DR
Netlify deploys static sites, this means dynamic sites like Wordpress sites cannot be deployed by Netlify. If you want to learn about the difference between these two then here is a good article.
The only way you could ‘convert’ a site to even be deployed by Netlify is by re-building it with a ssg and then add Netlify CMS to it by following this guide.
In my opinion, your best bet is to use a Netlify Template with Netlify CMS and just transfer the content from your current site over.