I'd reckon Armbian maintainers turn these on by default, you can grep for them (if you know the name of the mitigation symbols in the kernel) in /boot/config-*. E.g. the CONFIG_CPU_SPECTRE symbol on my Exynos-based Odroid XU4:
# grep -i spectre /boot/config-5.4.72-odroidxu4
CONFIG_CPU_SPECTRE=y
Apparently 5.10 comes with rewritten Spectre mitigation code for ARM64.