Update: a working Armbian image (both SD card and eMMC) has been made available from c0rnelius / pyavitz: https://github.com/pyavitz/binary/releases/download/images/rk3399-nanopi-r4se-debian-bullseye-5.19.11-arm64-2022-09-27.img.xz
Boot using an SD card (either the image above or the Armbian R4S image with my dtb file above) and run the following to image the eMMC:
wget https://github.com/pyavitz/binary/releases/download/images/rk3399-nanopi-r4se-debian-bullseye-5.19.11-arm64-2022-09-27.img.xz
xz -dc rk3399-nanopi-r4se-debian-bullseye-5.19.11-arm64-2022-09-27.img.xz | dd of=/dev/mmcblk2 status=progress
Note: if booting using pyavitz image from an SD card, you'll need to use a toothpick to press in the MASK button on the R4SE for 3 seconds during power on to use the SD card bootloader.