The package is not compatible with PHP 8.1 yet. There were a lot of serious changes in PHP 8.1: https://php.watch/versions/8.1 (see Deprecations in the bottom).

We've started to make php-imap compatible with PHP 8.1 but stuck on the following error when fetching emails via oAuth:

ErrorException: Undefined array key 2 in /vendor/webklex/php-imap/src/Connection/Protocols/ImapProtocol.php:593 

The patch with changes already made is attached. In order to see full error message we added echo $e; in Query.php on line 319.

php81.zip