DFRobot Router + CM4 (1GB RAM/8GBeMMC/no Wifi) - unsupported board

Hello all,
I installed an openWrt into my CM4 with eMMC (using rpiboot/rufus), but when I plug the USB cable into the DFRobot Router, ACT LED flashes 4 long and 4 short times after a short time. This repeats after a while.
No Luci interface at, no ssh, no nothing.
As I read somewhere else, this LED flashing pattern means "unsupported board".
Yes, CM4 and DFRobot board is good - tried to flash with other images (raspbian), and it worked like a charm with no errors.
I tried to use the DFRobot image from their wiki page, I tried also the factory CM4 image from OpenWrt site, but still 4 long and 4 short ACT Led.
Using powerful (3A) power supply, so no undervoltage for the board.

Please help me with this.