Hi FurmanSK,
I've builted a version of bootloader with 534Mhz ddr4.
So first make a backup of your installation and after
- download this bootloader https://ilmich.libreelec.tv/rk3328/u-boot-rockchip.bin
- flash it in your bootmedia (from a linux machine or directly in a ssh session of your libreelec installation)
where ${BOOT_DISK} is your boot device (for example /dev/mmcblk0)
If works you should see an higher pll_dpll in clk_summary.
Let me known.
Michele