Same problem here. 50 MB/s wite, about 250 MB/s read.
Brandnew Macbook Air M1. Lacie 6big 48TB.
This absolutely breaks my workflow. Honestly: Even if they fix it, I am not going to touch a Lacie product ever again. Its been a year since the release of M1. They should at least openly communicate incompatibility and admit their unwillingness to provide a solution.
Since I need to access all my video and photo files on a fast drive, I'll probably switch over my hard drives from the Lacie device into another enclosure. Bye bye Lacie.