Hello,
Royal users had problems with SEO title because it was duplicated. We have fixed this issue and I don’t remember the problem that users could not enable the Yoast plugin. Did you try to enable default WooCommerce theme like Storefront and then enable Yoast plugin? Does problem still persist? Also, can’t you enable plugin or plugin is enabled but you don’t see meta tags on the frontend?
If problem happens only when our theme is enabled we need detailed information about issue(your actions step by step to reproduce it, maybe screenshot for better understanding) and Dashboard and FTP access to your site.
So, keep me in touch if Yoast support finds that Royal is the reason of the problem.
Regards