WordPress Throwing Deprecated Errors on its own Files

These kinds of warnings happen when you run WordPress v6.1 or lower on PHP v8.1+. You should downgrade PHP to v8.0, or wait for WordPress v6.2 which upgrades the Requests library to add compatibility with PHP 8.1. ( WP 6.2 at the time of writing is in the release candidate stages )

Note that these deprecations do not happen on PHP 7.4. I saw you said that they do, but this implies you didn’t succesfully switch the site to PHP 7.4 and it may still be on PHP v8.1