Do devices on AC currents have flicker on and off?
Yes, it does. More precisely, AC current is a sine wave, and so the voltage and current smoothly pass through zero. In a purely resistive load, the current and voltage are in phase, and the power into the load can be described by the absolute value of \$\sin(t)\$. In reactive loads, the current will lead or lag the voltage, but both the current and voltage still pass through zero at some point.

For simple resistive loads, this is fine e.g. an incandescent light bulb receives pulses of power, but its time constant is much greater than 1/60Hz, so you don't see a visible flicker. Another example might be a slow cooker, which also has a time constant much greater than the line frequency.

For many devices (phone chargers, computers, etc), we use AC/DC converters that convert the alternating current to a steady DC current.

Several types of motors actually depend on the alternating current, as it determines their rotational speed by alternating the current through the windings.