you need to flash patch bl2 img for BPI R4 8GB
The second option works with any OpenWrt version and allows to use the full 8GB:
I used the official OpenWrt Firmware Selector and picked the latest stable release, 24.10. After selecting the packages I needed, I wrote the image to an SD card and used it to install OpenWrt to the NAND using U-Boot, and from NAND to eMMC.
This results in OpenWrt 24.10 being installed to eMMC (also on SD and Nand) but initially, only 4GB of RAM is detected.
To fix that, I booted OpenWrt again from NAND and re-flashed the BL2 partition of the eMMC using the bl2_emmc_8g.img file (same one included in the snapshot 21.02 files I mentioned above).
Here’s the process I used while booted into NAND:
echo 0 > /sys/block/mmcblk0boot0/force_ro
dd if=bl2_emmc_8g.img of=/dev/mmcblk0boot0
mmc bootpart enable 1 1 /dev/mmcblk0
After rebooting from eMMC, the system properly detected the full 8GB while still running the stable OpenWrt 24.10.