I have a G-Speed Shuttle RAID which also wouldn't mount on my M1 MacBook Pro - very disappointing. There is nothing on G-technology's website to help out. I managed to get it to work by downloading the new driver (R_MacDrv_V6_2_16) from the Promise website,
I think all the drivers are the same on that page.
The G-Speed made use of the Intel Ktext and now they have re-written it to work with M1 Macs. The install involves lowering the security at boot to load a non-Apple extension (there are very clear instructions downloadable from the Promise website) but quite frankly to get the RAID working, that's not a problem. It now works like it did before without issue for me - phew! I hope this helps as it was driving me nuts.