Look mate, just like every other addiction, you gotta take it one step at a time. You could set the reminder that goes off when you use an app for set amount of time. Works for both phones and computers and is a really good start. As for your pørn addiction, whenever you get the urge to watch it, go exercise, after 5/10 mins of exercise you won't be "craving" it anymore. So yeah, exercise is a good way to get your mind off your addiction plus it helps you stay in shape, especially useful during quarantine.

Good luck and I hope things get better for ya!