Same problem here. M1 Mini, 16GB, Big Sur 11.2.3, LaCie 6Big with 20 TB Raid 5 connected via TB3.
A few days ago I installed the new driver and Raidmanager 2.9.3.207, at least the raid was accessible via TB3 write: around 31 MB/s
read: around 460 MB/s
Today, April 11, it seems there was an update for the kernel driver but no speed changes.
cbl-
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