How to fix slow website which has fatal error?

Question

PHP Fatal error: Uncaught Error: Class "Yoast\WP\SEO\Helpers\Social_Profiles_Helper" not found in /home/mky89yyr/public_html/sivu/wp-content/plugins/wordpress-seo/src/generated/container.php:3354

in error lod there is multiple different fatal error with elementor, yoast seo and astra. Besides that there is also this:

PHP Fatal error: Uncaught Error: Failed opening required....

How to fix these? What the stack trace mean? Is it the instruction to fix it? I don't get it.

I have done these already in Wordpress:

• optimized photos
• installed w3 cache
• deleted unnecessary pluggins and media