ATTINY84 cannot get PWM to work at all
I think your issue may be the choice of waveform generation mode.

Looking at the datasheet (extract from page 83):


You have set bits WGM02 and WGM00 so you are using mode 5. You can see that in mode 5 the timer TOP is at OCRA, so the timer is counting from 0 up to the value you have written into the OCR0A register, but then resetting to zero before the pin output has a chance to go low, so you have 100% duty cycle PWM.

Using mode 1 should work as expected, as TOP is at 0xFF so the timer will count from 0 to 255 each time and give the 8-bit resolution fixed frequency PWM output you expect. Just don't set bit WGM02.

Also as an aside: I think you second for loop has an issue. The test condition is that i is >= 0 but this will always be true for an unsigned integer as it will wrap around from 0 to 255. Using a signed integer type like int16_t would work, or you could test for > 0 which will become false once i equals 0.

Hope that helps.