Both our kids have done this over the past 20 yrs.

Easy (pricey): Patio curtains not vertical blinds and try to find a sturdy set made of metal not plastic so it can handle some yanking! I like the ones where you slide the curtain pole through a circle in the three brackets. It’s super strong and can’t be yanked down. I’ll rephrase that, “easily yanked down”!

Complicated (cheaper but may not be if your kid is “stubborn OCD”): We we’re lucky with our daughter because our apartment faced a very busy road that was 1/8 mile away. So what’s the chances of a “50MPH High speed Peeping Tom!”. But people walking along the walkway could look up and I’m not into the “Family Review”! We stapled a very large piece of opaque window film up (temporary), a nice solid color king or queen bedsheet will look acceptable if the apt. complex is a worry. Keep the horizontal bracket up and pull all the vertical blinds off and put them aside, buy some more (you’ll need them trust me). Leave it alone for a week or two. Both of my kids OCD issues tend to only last a few days to a few weeks when they thought they won the fight. At our house my wife wanted both curtain and verticals and we faced the back neighbors looking in at night (I CAUGHT THEM SEVERAL TIMES...(wow, I just sounded like a nut job there!)) After a week or so just put one vertical up a day. A paper stapler or small piece of duct tape is a good way to fix the “split not totally broken” slats so you can maybe get 2 or 3 tries out of each ($$$). Before long you win. Crazy part was after my son stopped caring about it anymore our golden retriever would plop down near the window on warm days and pop them off and he started my son up again!!! Uhhhh!
Hope that helps!

1: keep calm and don’t tell him to stop. He’s likely doing it to get your attention.

2: work on removing the temptation. When he’s not around, put sonething in front of it that will obstruct his access to it. You might actually have to open them when he’s home.

3: Redirect the behavior to something else. Provide him with something else that he can play with appropriately. At that age we used to have an indoor tent but I also recall making “forts” put of couch cushions or blankets over the kitchen table.

4: transform the behavior. Interact with him and demonstrate appropriate actions associated with the new item or activity.