The change has been done in release 21.1.4. No need to manually add it.
On an HP laptop with Window 10 pre-installed, doing this made Windows unbootable. However, I didn’t care, because I did not want to dual-boot, but rather use the entire storage for Manjaro. After disabling RST, I formatted both “drives”.
They appear as separate drives in the BIOS and under Manjaro after disabling RST, yet these two storages really exist in a single physical device.
/dev/nvme0 and /dev/nvme1 are both on the same physical device. I installed Manjaro’s root system on the much smaller nvme0, and placed /home on nvme1.