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What version of MongoDB is your Atlas cluster running?
The MongoDB PHP 1.3.4 extension was released on 2 Dec 2017 and is more than four years old now. My first suggestion would be to upgrade to the latest version of the PHP extension which is compatible with your MongoDB server version and PHP runtime.
According to the PHP Extension Language Compatibility reference, the latest extension version supporting PHP 7.0 is the MongoDB 1.9 PHP extension. The most recent 1.9 release was 1.9.2 in July 2021.