this is really weird. #steam on #chachyos #linux lets me add my old SATA SSD after converting it to ext4, but it's not letting me add my NVMe over 20gbps USB C as a BTRFS filesystem with a mountpoint specified in /etc/fstab. It added just find as NTFS before. Just games would not launch without a strange write error.
As for why I'm using a 20gpbs USB C to NVMe adapter: My Gigabyte B-550 Vision D motherboard does in fact have a second NVMe slot. It's disabled when the lower most PCIe slot is in use, which it is, for a USB header, to get my front USB3 port working. I still hope to use PCIe 8x - 8x bifurcation for... something. I do have an AMD Radeon 6650 XT lying around. But I want the thing to work the same as they did on Windows first. Steam on Windows had no complaints about my external NVMe drive.