LED intensity issues on Attiny85 with 74HC595 to control 8 LEDs
74H5C95 has 6mA output with a 5v supply according to the datasheet. If you want to run your LEDs at 20mA, you will not be able to with just the shift register. You could use a transistor for each LED as a switch controlled by the shift register pin and the other pins of the transistors attached to your supply voltage if you are married to the 74H5C95.