HP Victus 16-s0000: Internal display and keyboard backlight flicker to

I have an HP Victus 16-s0000 laptop. The internal display and keyboard backlight flicker together, but the laptop works normally on an external monitor.

Symptoms

Screen and keyboard backlight flicker at the same time.

External monitor (HDMI) is stable.

The laptop still runs normally otherwise.

USB power load (charging a phone) sometimes makes the flicker worse.

Initially, doing an EC reset / power drain (holding the power button ~40 seconds or disconnecting the battery) temporarily stopped the issue.

Recently, the reset no longer stops the flicker.

What I’ve tried

Updated BIOS to the latest version (F.31).

Reset BIOS settings (CMOS reset occurred).

Performed EC reset by disconnecting the battery and holding the power button.

Checked battery health (about 77% capacity remaining).

Tested with an external monitor (no flicker there).

Question

Since the keyboard backlight and internal display flicker together, could this indicate a power rail / embedded controller issue on the motherboard, or could the battery or battery management circuit still be responsible?

Any advice on what component or area of the motherboard to inspect next would be appreciated.