I would read from the first post “4. Please update the SPI flash to the latest SPL/U-Boot binaries if you would like to try nvme booting (set boot mode as QSPI boot).” as you do not need to, but you probably should anyhow, upgrade the SPI flash if you do not need NVMe to boot.
Why would StarFive provide a newer version if it was not meant to be upgraded ? It is only 5 commands if you are upgrading from the previous version.
EDIT: There were 83 commits to the StarFive U-boot between v3.04 and v3.6.1, six were related to PCI and two were related to NVMe. I would see that alone as a reason to upgrade if you were using NVMe.