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The kids get 30 minutes (max) of open-ended screen time per day. This can be watching a show, playing a video game, whatever they want (that's age-appropriate). Their current obsession is worm / snake games (e.g. http://wormax.io/ ) which are really just Tron Light Cycles, or to go even farther back, Surround (for the Atari 2600), but much better. (and regarding the single vs multi-player discussion: these snake games are multi-player and you can "friend" people to form groups, but I don't think there's any communication between people; and our kids play at the same time so they're playing with each other as well as with people from all over).

Reading time is mostly unlimited. While we do have lots of books, the kids have read them enough and want more. We used to go to the library weekly but that's much more difficult now due to COVID-19. We can still get books from the library, but not nearly as much or as often. So, tablets give them access to thousands of books and that really helps. (more on this in a moment)

Programming/creative time: generally no more than 2 hours at a time. Might do more than 2 hours in a day, but needs to be broken up with going outside, reading, lunch/dinner, etc. The kids have really gotten into Scratch (Google and MIT project, I believe). It's really cool, and a great way to get kids into programming (there's also https://code.org/ and https://bitsbox.com/). With Scratch time we sometimes require an hour of programming / creative time before they can play games. But playing Scratch games isn't really treated as video games because they end up finding something they want to copy (either part of a game, a technique, or maybe an entire game to modify) and it leads to creative time in a natural way. That, and video games do help with hand-eye coordination (another reason to prefer them over passively watching TV).

Outside time: weather permitting, the kids are required to run around outside for 30 - 60 minutes per day (play soccer, tag, catch, whatever).

For the books, and partly for the video game time, we have Kindle Fire Kid's Edition tablets (from Amazon). Kid's Edition comes with a year of Freetime Unlimited which can be renewed for something like $75 - $80 per year after that. "Freetime Unlimited" has worked out well for us because not only does it provide access to thousands of books (and tons of games if they want to use the tablet for game time, but lately it's all about those snakes), but it also lets you limit the amount of time they can use the tablet, and for what types of activities. So we set them up to be 30 minutes max for games/apps, unlimited time for reading, and 0 minutes for movies, and no web/browser access (I do recall one kid coming home from school, 3rd grade, telling us that a classmate had watched DeadPool 2 on their tablet as the parents weren't home and the babysitter wasn't paying attention; good movie, though not as good as the first one, but certainly not for 8 year olds).

As a consequence for fighting, being mean, and so many other "fun" things, we deduct minutes from the video game time (we deduct from the initial 30 minutes). The effectiveness of this varies per child, of course.

As a reward for going above and beyond, we will add minutes to video game time (sadly, though not unexpectedly, this does not occur nearly as often as minutes getting deducted).

We're able to control the device usage since all laptops and tablets stay in the living room (they'll just need to wait to see DeadPool, at least until highschool when they'll get more privacy ;-)

None of this implies a lack of doing other things, such as Legos, arts + crafts, reading physical books, playing board games, yelling at each other about the most nonsensical stuff, etc

Also keep in mind:

1. "Screen time" isn't just when they are individually looking at a screen. We count watching TV / videos / YouTube / movies / etc as a group as screen time (mainly to make sure that we remember to factor it into a general sense of how much time in a day is spent sitting and watching). Educational videos (The Science Asylum is a favorite, and several others) and some computer games (e.g. Kings Quest I: Quest for the Crown and other similar games) have worked out quite well.
2. For many / most of us, kids will be online for the first few weeks of school (possibly longer depending on how things go), and that is plenty of time sitting and working on a device, even if it is educational and sometimes interactive.
3. There was some discussion on another answer regarding time spent playing with LEGOs being somewhat equivalent to time spent playing Minecraft, because they are both creative and similar type of building. While I think Minecraft is really cool and has many positives, I think there is a clear distinction between these two, and that equating them ignores some important stuff. Yes, both are creative and deal with spatial relationships and some hand-eye coordination. However, Minecraft is less movement: you are sitting in one spot and using a mouse (right? I haven't spent much time on it). With LEGOs, there's a HUGE variety of pieces, it's much better for fine-motor skills and dexterity, there is much more flexibility in what can be done considering what is built can interact with the real world, you can fit pieces together in non-ideal ways and/or integrate with non-Lego stuff, you get up and move around more, etc. Just sayin.