I just installed official openwrt with plain luci. Everything worked. Just had to set up DHCP interface for WAN under interfaces.
Flashed this version with balenaEtcher.
How to flash: Getting Started - Seeed Wiki
Firmware: [OpenWrt Wiki] Techdata: Raspberry Pi Foundation Raspberry Pi Compute Module 4
Works good so far, will see in a couple of days how the throughput works, had problems with decreasing throughput until I rebooted it. I want to use this thing as a router and nothing else.