Thanks so much for the reports of these notices on PHP 8. I've marked this as something for our developers to have a look at.
Note that those reported notices are not "errors" so much as deprecation notices. You should turn off the display of those notices on production sites with something like this added to the wp-config.php file:
// Turn debugging on
// Tell WordPress to log everything to /wp-content/debug.log
// Turn off the display of error messages on your site
// Hide general PHP errors