The activity trigger exists but is not documented in the LED binding.
A patch was sent to document it but wasn't accepted.

The intention of the LED is to show if the system is busy or not
so the cpu trigger is good enough so switch to that to clean up
the warning.

Link: https://lore.kernel.org/all/20210923065500.2284347-4-daniel@0x0f.com/
Signed-off-by: Daniel Palmer <daniel@0x0f.com>
---
 arch/arm/boot/dts/sigmastar/mstar-infinity-breadbee-common.dtsi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/sigmastar/mstar-infinity-breadbee-common.dtsi b/arch/arm/boot/dts/sigmastar/mstar-infinity-breadbee-common.dtsi
index 71da10d9228f..0f03f471a344 100644
--- a/arch/arm/boot/dts/sigmastar/mstar-infinity-breadbee-common.dtsi
+++ b/arch/arm/boot/dts/sigmastar/mstar-infinity-breadbee-common.dtsi
@@ -35,7 +35,7 @@ leds {
 		compatible = "gpio-leds";
 		led-red {
 			gpios = <&gpio MSC313_GPIO_SR_IO16 GPIO_ACTIVE_HIGH>;
-			linux,default-trigger = "activity";
+			linux,default-trigger = "cpu";
 		};
 		led-yellow {
 			gpios = <&gpio MSC313_GPIO_SR_IO17 GPIO_ACTIVE_HIGH>;
-- 
2.51.0