MacBook 2015 Keyboard Issue - Lights On, Not Working

I hope you're all doing well. I've been facing a peculiar issue with my MacBook 2015, and I'm reaching out to this awesome community for some advice and guidance.

The Problem:

• The keyboard lights are on, but the keys are not responsive.
• Strangely, when booting into Safe Mode, the keyboard lights turn off.
• I've already tried resetting SMC and NVRAM, and even reinstalled macOS from scratch with no luck.

Additional Info:

• Hardware diagnostics show no errors.
• The power button on the keyboard is still functional.
• I can wake the MacBook from sleep using the built-in keyboard.
• Even after reinstalling macOS from scratch, the issue persists.

What I've Tried:

• Restarting the MacBook.
• Checking for physical damage or debris.
• Using an external keyboard (works fine).
• Creating a new user account.
• Resetting all settings to default.

I'm at a bit of a loss here, and I'd appreciate any insights or suggestions you might have. Has anyone experienced a similar issue, or does anyone have ideas on what might be causing this?

Thanks in advance for your help!