Because of differences in the hardware for the SMA 7210 and SMA 6210 they are not supported by 12.1.0 firmware prior to the 12.1.0-05477 hotfix version.
As a result, new SMA 7210 or SMA 6210 hardware ships from the factory with 12.1.0-05477 as the base firmware.
In addition the SMA 7210/6210 hardware is not supported in the 12.2.0 firmware version, so that upgrade is blocked.
This hardware is supported in 12.1.0-05477 or 12.4.0-02223 and newer hotfixes on these versions. Future firmware versions will support this hardware, e.g. 12.4.1.
Note: 12.3.0 firmware, from version 12.3.0-02939 on, supports this hardware, but all support for 12.3.0 firmware ended on 31 JAN 2021.
https://www.sonicwall.com/support/product-lifecycle-tables/sonicwall-secure-mobile-access/software/
Do not be concerned that new or RMA SMA 7210 or SMA 6210 is found to have firmware version 12.1.0-05477.
This is required to support the hardware differences from the older SMA 7200 and SMA 6200 hardware.