It is possible to add horizontal lines to moving averages? for example if you right click, volume or rsi, i'm able to add a horizontal line. if it isn't a feature as of it, it would be great to add horizontal lines to moving averages as we'll. thanks!

You would add the horizontal line to the scale of whatever is being averaged instead of the moving average.

If you want to plot the moving average as a horizontal line, you can change the Plot Style to Last Value Horizontal.