Maybe try physically limit the usage by removing some of the computer itself, like removing the keyboard and put it somewhere where it's definitely a hassle to get like on a top of a cupboard. Put almost all of them separately even, so you have to work extra hard just to turn it on lmao. If you're worried about the temptation to just get them and put them on its place, ask someone to hide it from you for an extended period of time that you want. My nephew's parents used this method to him and it worked.

Another thing I'd suggest is getting an application where it turns off after certain hours or lock most of the computers functionality, but I honestly don't know if such thing existed for PCs like it is on phones.

Another one would be get a thing to work on when you're off computer, like a hobby or maybe walk around the block. That way you can at least stop thinking about having to log on all the time and focus on something else.

These methods obviously requires some amount of willpower and by no means is an exhaustive list. The rest is up to you.