Personally, I am not a fan of screen time rules, mainly because I think that for most children (who aren't ND, and don't have naturally addictive personalities) content type restrictions work better.
I feel terribly sorry for young kids. I personally think what many parents do (with good intentions) is actually really unfair.
What we say is:
"Here go on these addictive apps, games, platforms. Oh no - you are addicted! Right, now you can only play these addictive things for 1 hour a day. so you won't get addicted"
For me, the root of the problem is the type of content, the time spent on it is a secondary effect. What I mean by that is that I believe it is the change in content + delivery that has created screen addiction problems, not the screens themselves.
For example:
20 years ago, video games were frustrating and hard, lower quality, lower graphics, less exciting, and multiplayer was only local. So "most" kids would play a bit, get frustrated and stop for a while. They would play when their friends were round, but then be more likely to stop when they left etc. A simple low-res 2d game wasn't overwhelmingly better than toys...
Today, video games are designed from the ground up to target young children, be easy and accessible. Full of highly addictive mechanics that keep you always wanting more, reward hours of play rather than strategy, and are online so social play is endless and always.
20 years ago, TV shows were one once a day or once a week, and then a different show came on, so kids would naturally finish their show and move on. Families had 1 TV, so parents would change to something they wanted and the child would go off to do other things. Kids shows were mostly shown at specific times of the day.
Today, Netflix and the like have endless shows that autoplay through massive series and playlists. There is always exactly what your kid wants, all the time. And the next episode will start loading straight away, making it hard for them to switch off.
etc. etc.
I could go on about smart phones, social media, short videos and more, but I think the point is made: it is the addictive and endless nature of technology that causes the problems, not really the technology itself.
So for me, I think most screen for (younger) children can be solved by avoiding these addictive dynamics.
1, Only normal live TV, no streaming apps.
2, If you want video games, single player, and perhaps older/simpler games without addictive mechanics
3, No personal device/tablet, only family TV, family computer etc.
4, No online connectivity
etc.
Remove the addictive components from their lives, and in many cases, you won't need to worry about the time.