I get what you're saying, but "the internet" has evolved alot. Even knowing the dangers that are present, and how marketers try to short-circuit your brain etc etc (which we did do, I'm very clear with my kids that every law needs an explanation and they are provided with explanations) I think 13 is still too young to be left alone. Really I don't believe there is a minimum age, it's more who can resist addictive behaviors, so you tell me.
I'm not going to presume your age but at least when I was growing up, the internet was more like a giant flea market: you go in, and yes there could be things that might be bad or useless or creepy or diddly, and you really learn where the quality stuff is by poking around. Internet then was very analogous to going out into the real world where you learn risk through experience and can walk away. With the walled gardens we have today?... it's more like dropping an open kilo of cocaine in front your kid, saying "you can snort it, smoke it, shove it under a toenail, put it on your wee-wee and it will make you feel good for a bit, but then really, really, really bad. So be careful" then turning on a fan pointed in their direction as you walk out of the room... Everyone working on user engagement at FB, TikTok, Insta and the rest, they know how to keep you on with dopamine hits. The second a kid logs in, the hyperoptimization forces the most addictive, useless crap in their suggestions or feed no matter what their search is, such as the box opening junk, or mash-ups that don't have anything but popular characters giggling for 2 minutes, and it gets weird in a hurry [0]. And no matter how hard you try, there are always more suggestions that take you into a corner of dopamine hits than quality information, and it's very difficult to tell the difference. It's unavoidable, and to say "just let them learn the dangers" just tells me you need to observe a kid while they navigate (it always ends in a sinkhole) or one who just put the tablet down. I'm not going to presume your life experience, but I know someone who's jonesing for a hit when I see one.
I highly recommend you try setting up fake child accounts (minimum age, or if you want the full experience, set up a Family Link and say you're 8) on YouTube, TikTok, and the rest. There is no chance for a learning curve, there is no chance for evaluation. It's just immediate click-and-addict.
These are the new cigarette companies and I'm treating them as such. In my case, we're learning as we go along. So she can use the laptop for writing (podcast scripts, stories and essays), research for school and any activities/hobby with one of us in the room to help with tips and, as we put it, help to make sure the algorithm doesn't short-circuit her brain), and introduce her to coding by making her own Roblox games (played locally). The tablet is for listening to podcasts and recording her own episodes/thoughts and there are good drawing apps.
As to how we're going to approach things moving forward... Awareness is key but at least with drugs you can say no and not ingest. When she's in high school, just saying no is probably not a viable option, so we're still figuring out and trying to learn what works for others.
[0] Video is 5 years old, and the weirder did is probably gone, but the gaming the algo is still valid https://m.youtube.com/watch?v=LKp2gikIkD8