Hi,
I think we did not enable the CEC pin in the device tree. You can enable it with the following patch and try. I am sorry we don’t have a TV with CEC in the office so we can not test for you.
diff --git a/arch/arm64/boot/dts/rockchip/rockpi-4b-linux.dts b/arch/arm64/boot/dts/rockchip/rockpi-4b-linux.dts
index 9370a8d..217d8e0 100644
--- a/arch/arm64/boot/dts/rockchip/rockpi-4b-linux.dts
+++ b/arch/arm64/boot/dts/rockchip/rockpi-4b-linux.dts
@@ -295,6 +295,8 @@
#address-cells = <1>;
#size-cells = <0>;
#sound-dai-cells = <0>;
+ pinctrl-names = "default";
+ pinctrl-0 = <&hdmi_i2c_xfer>, <&hdmi_cec>;
status = "okay";
};