Debugging a dimmer circuit (TT6061A)
The TRIAC is probably shorted.

Did you have a light bulb burn out?

What happens with filament bulbs is that the filament burns and separates in the weakest spot.

If you unscrew the bulb, then motion causes the free end of the broken filament to flop around.

If you unscrew the bulb with power applied, then the filament can touch the opposite post in the lighbulb and cause the bulb to "flash" briefly and since the filament is shorter than normal, its resistance is lower than normal and it draws a lot of power.

This condition can blow out a triac.