Anything in a Thunderbolt enclosure will report back to the Mac as a proper PCIe device. From a hardware level, the RAID card would continue to work but I can't vouch for any drivers being Apple Silicon compatible. I have a two NVMe drives in a RAID 0 in a Sabrent Dual Enclosure over thunderbolt with the array being managed by macOS. So that works, and I would recommend getting a drive enclosure rather than a PCIe chassis in your case for cost and simplicity.
My external NVMe drives are actually slowed down by being in RAID as the Thunderbolt bus is a bottleneck and they have to deal with RAID overhead. They would be faster as separate drives in separate enclosures. I already had the drives from my previous hackintosh and this was a solution intended for capacity and good enough performance.
Thanks for the reply.
My RAID card is High Point SSD7101A-1 and it is compatible with even the current OS. In order to do so Highpoint has new drivers. I think encryption though is a problem (which isn't an issue for me).
I guess I'll check prices. My card is still sold but it has been superseded. I presume it might be worth a little bit. Highpoint say:
"HighPoint Thunderbolt 3 products, such as the RocketStor 6661A PCIe Expansion chassis and RocketStor 6662A Hardware RAID Enclosure, require x4 lanes to perform optimally. These devices are capable of delivering up to 2800MB/s of transfer performance using a Thunderbolt 3 connection. "
Highpoint stresses not to use a T-4 enclosure as they are slower for data.
But the cost of their PCI adapter is in my dollars, $Au608. While a single T-3 NVME drive enclosure, seems to be around $180, for a brand I have not heard of. Presuming my RAID card is worth nothing, with a cost of three external no name branded T-3 enclosures costing me $Au540 (Australian dollars) I think I'd be better off with a PCI t-3 enclosure, and then trial whether RAID was worthwhile.
In my Australian situation, I could add another 2 TB NVME cards I(so an extra 4TB) to the RAID card (which already has 4TB) in its (new) external enclosure, for $Au340.
So for me to get 8 TB (but maybe RAID would work poorly) would cost me $Au950. And of course some hassle. Plus OS upgrade issues too. Meanwhile the Apple solution for me would cost $Au2,200. Less the cost of me selling the card I have and its two NVME 2 TB cards. If I got $500 the 2 x 2TB cards and the card itself, then the overall cost for me would be an extra $Au750 to get 8TB inside the Apple Studio. Despite it costing a heap for memory. As shown below.
Apple's storage costs a lot more. Using NVME cards, the cost per TB for me is around $Au88 per TB. In comparison, Apple charges
The cost for me with a Studio using its (very fast though) internal drive options are:
1 TB: $Au200 - Price per TB is $Au200 v $Au88 per TB (WD Black NVME M2 770 $Au88)
2 TB: $Au600 - Price per TB is $Au300 v $Au88 per TB (WD Black NVME M2 770 $Au176)
4 TB $Au1,000 - Price per TB is $Au250 v $Au88 per TB (WD Black NVMEs M2 770 $Au350)
8 TB $Au2,200 - Price per TB is $Au275 v $Au88 per TB (WD Black NVMEs M2 770 $Au700)
In my case I suspect I'm better to get worse CPU performance and have more disk capacity. After all the base m2 Studio will be a lot faster than my 5,1 Mac Pro ...
But gee ... going to Windows would save me a lot ... I could pop my card in and add some cards for $Au350 and therefor save $Au1,850. I imagine the computer would cost less too ...