check your php version. it is likely you dosnloaded a wrong pecl redis file.

visit https://pecl.php.net/package/redis/6.1.0/windows and ensure that the version you download matches the version there.

then based on your system setup, correctly download either the ts or nts file. in my case the ts was needed.

e.g php_redis-6.1.0-8.2-ts-vs16-x64 (the 8.2 is my php-version)