What exact enclosure are you using?

OWC Express 1M2 (Thunderbolt 5, single M.2 NVMe) — three of them, two on the Mac's own ports and one behind an OWC Thunderbolt 5 hub since the machine has three ports.

Each enclosure tops out at about 7.1 GB/s on whole-file reads regardless of the drive inside (a 2 TB SN8100 measures the same as the 1 TB);

the drive behind the hub reads 5.7 GB/s and falls with queue depth.

Details in the README's hardware section