NVMe speed ratings are based on a direct internal connection (an M.2 slot). In an external enclosure over USB 3.2 Gen 2 (10 Gbps), speeds are lower, which is expected. To get the best results: make sure the drive is formatted (APFS or exFAT), and plug the enclosure into a USB-C port that supports 10 Gbps or more (USB 3.2 Gen 2, Thunderbolt, or USB4). You can also try a different SSD, reformat the drive, or connect to another computer with a fast USB-C port. Keep your system updated, and restart after removing other USB-C devices.