Anyway, there are 2 errors in the code:

- You don't enable the reset after interrupt

try to add:

if(count>5) {
while(true) {} // Should reset after 2 seconds
}

in loop, and you'll see no reset.

To fix change the line with:
WDTCSR = (1<<WDE) | (1<<WDIE)| (1<<WDP2) | (1<<WDP1) | (1<<WDP0);

- Watchdog interrupt must be enabled after every interrupt (or you'll see a reset every 4 seconds)

To fix, add in loop:

WDTCSR |= (1<<WDIE); // Enable watchdog Interrupt again

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