I have the same notice: Deprecated: Return type of Requests_Cookie_Jar::offsetExists($key) should either be compatible with ArrayAccess::offsetExists(mixed $offset): bool, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice.
Reverted back to PHP 7.4 from PHP 8.1, message disappeared. But the WordFence plug-in still does not scan any files. But that’s a different issue.
[May 25 22:25:26] Scan Complete. Scanned 0 files, 14 plugins, 3 themes…………