Moving to OpenWRT is actually supported by Cudy, just a sysupgrade:
Cudy Software Download (cudytech.com)
Not sure if you can use a vanilla OpenWRT (snapshot or 25.03.0) sysupgrade image from stock. Just to be on the safe side, I did the following:
Upgrade to latest official firmware (1.16.2) → Cudy OpenWRT sysupgrade → 25.03.0-rc3 sysupgrade.
There's a thread in the forums: Support for Cudy WR3000 - For Developers - OpenWrt Forum