mysql CPU load

If you have a lot of content, then wp_posts and wp_postmeta could get quite large. wp_wpr_rucss_used_css is not a standard table, but appears to be from the WP Rocket plugin. They have an article discussing it’s size here: https://docs.wp-rocket.me/article/1627-database-size-increases-with-remove-unused-css?utm_source=help_center&utm_medium=wp_rocket

Many of Google’s Pagespeed recommendations are not for your benefit, they are to make it easier (and less costly) for Google to scrape sites. Their recommendation about usused CSS is clearly in that category.

I suggest that you disable the Remove Unused CSS option in WP Rocket, and truncate the two tables it uses if disabling the option doesn’t do so. This (anti-)feature is converting client-loaded CSS to server-generated CSS, and potentially causing server issues in the process.