Hi there, welcome to WordPress Trac! Thanks for the ticket.
I'm sorry to hear you are having issues with your website since the latest update. Unfortunately, it doesn't look like there are any actionable items for WordPress core here, as website performance depends on many various factors.
Here's the full list of changes in 5.7. If you can identify a performance issue with a specific change, please feel free to comment and provide some more information, so that the issue could be investigated further.
Until the issue is identified, confirmed, and can be reproduced with some steps on a clean install in more than one environment, this topic is best discussed on support forums.