I have been trying to solve my issue with Lacie 5BIG TB2 and Big Sur on iMac for 2 months. When accessing the Lacie Raid Manager, I would get the message that a driver needs to be installed. When I manually ran the install script, I noticed that I was getting an error when trying to load the driver. I noticed some references to old kext. I use the System Report to look at all non Apple extensions and see when they were installed, if they were loadable and x64. I opened a terminal and sudo su cd /Library/Extensions deleted all old extensions that I no longer needs such as Blackberry, Epson and Logitech. (rm -rf {name of the directory you want to delete} I then received a notification from Security and Privacy about something was updated (don't remember the exact message) and needed to restart my iMac. I restarted my iMac and to my surprise my Lacie 5BIG TB2 came back online :-) Bottom line for me, there was an extension that prevented others (like the Lacie one) to get loaded. Cleaning up these old extensions did the trick. Hope it can help some of you address that issue.

Bluedisk, unfortunately my work around only works for older Mac that had a number of OS major upgrades. It will not work for a brand new machine or brand new clean installation. The fact that you cannot access the Extensions directory means that you have not installed any non-apple extensions. My work around demonstrated that 5BIG works on Big Sur with an intel chip. Your Mac mini is based on the M1 chip and will need a different driver.