Two toddlers, one girl in elementary school.
By default, minimum limits. I want them to build habit and willpower themselves so they don't indulge as adults like many of my friends did in college.
No limit on TV. But I remind them there's a cost. Sometimes we play outside and leave the TV watcher. Sometimes we go upstairs and play in the bedroom. The family has fun without devices, but if you want to watch the same movie again, it's up to you.
Phone has tougher limits. Screen time before 5 PM on a weekday, 6 on a weekend. The earlier you wake up, the more screen time you have. The TV rules still apply: if you're on your phone in your bed all day and we had an awesome breakfast together, it's your fault for missing out.
No devices before a shower. My kids all get showered by 8 AM now, without any fighting. We had a lot of arguing and dragging them to the bathroom before this rule.
If your homework isn't done, stricter phone restrictions, or TV only. Homework causes stress and TV is a great cure, so I think it's fine. Gaming causes stress though, so they have to watch out.
YouTube has a lot of great stuff. My eldest learned every flag and capital city all on her own from YouTube, by 8 years old. My 3 year old knows her alphabet, and the 1 year old can recognize letters and numbers. But it only works if you let them.
The real restrictions are on what they watch and now when.
Kids imitate things a lot. So they can pick up really bad habits from a lot of popular YouTubers like screaming and panicking. Or sometimes even Peppa Pig can be a bit too sassy.
Pay to win games are also a problem. They purposely build addiction and then charge you later. They tend to not sleep, eat, etc and quit the game feeling miserable. You still want to expose the kids to them a little so they build immunity to that crap, but keep a safety valve on.