You likely have a NAND flash chip (not eMMC). Android 9.0 struggles with old NAND. You must use a MultiDownload configuration (scatter file) instead of a single update.img . Look for "RK3229 NAND Android 9" on FreakTab.
Android 9.0 on RK3229 offers a range of features, including: Rk3229 Android 9.0 Firmware
Enhanced dual-band Wi-Fi (2.4GHz/5GHz) and more reliable Bluetooth 4.0+ connectivity. Performance Fixes: You likely have a NAND flash chip (not eMMC)