Just to be clear: this is not 5.10.66 LTS from kernel.org but some forward ported 2.6 kernel, details here.
As such even the 5.10.66 string is pure cosmetics since to really ensure that RK’s 5.10 BSP kernel is identical with 5.10 LTS someone would’ve to rebase the Rockchip code on top of a clean 5.10.66 LTS. If this didn’t happen nobody knows how far away this RK 5.10 is from 5.10 LTS.
Does that mean going from 5.10.69 to 5.10.123 some of the LTS backports to 5.10 do not apply cleanly and you skipped them?