I’m pretty sure those “results” are simulations because the Arduino isn’t synchronized with the AC frequency and that’s not exactly what you’re going to see.
Not really. As long as you read a high periodically (i.e. once per cycle) the AC is present. You simulation appears to only show the switch-on (voltage present) state.
In the 1st circuit the LED will be off half of the time so it won’t appear as bright as the other circuits. BTW the LED will probably be too dim with a 10K series resistor. You might try 1K or you can go lower but I haven’t checked the current capability of that opto-isolator.
You can get rid of the existing 1K series resistor and connect the Arduino directly to the opto-isolator.
I’d go with the “simplest solution” - You can put a reversed diode or LED in parallel with the opto-isolator input to protect it.
If you put an LED on the opto’s input you can eliminate ALL of the circuitry on the output-side by enabling the Arduino’s built-in pull-up resistor. You might have to find an example of how to wire it. With a pull-up instead of a pull-down the Arduino will read low when the opto turns-on so you’d have to reverse your software logic.