I'm a game developer & a parent of 6 children. I would not outright give a child that young their own game system. I would definitely not give them unfettered use.
This is how I feel. My eldest will be 6 in October, and she's only recently started expressing an interest in playing games. She's picking them up fast, though.
We bought Animal Crossing New Horizons for my Switch (which is docked by the main TV in the lounge) intending to play it as my character with her helping, but she quickly got the hang of it, so she now has a child's account and her own character on the island. She can basically everything you need to do in-game, from interacting with the shop to managing her inventory, but she gets turned off by the large volumes of text in some interactions. To be fair, so do I. Some of those Blathers conversations are ludicrously long.
She asks to play it a lot now, but my wife and I don't let her play unless we're also in the room with her. She has an old laptop she uses for school work, but again, she's not allowed to use it alone.
But here's the rub: she's a neurotypical child with a few quirks, and she's typically well behaved, but even she finds it difficult to understand why she can't just play Animal Crossing all the time. She likes it. She thinks she's being productive weeding and collecting shells to sell to Tom Nook. And that's a hard thing to "get" as a kid. Hell, it's a hard thing for adults. I'm nearly 40 and I still drink more than I should sometimes, don't have the best diet etc. I think we've done a decent job of managing it so far, but I can tell there's a day coming where she's going to try and stand up to me or my wife and say she wants to keep playing after her 45 minutes or so is up.
I can't imagine how difficult it is to convey all that to a child on the autism spectrum.
So yeah, I'm afraid I don't have any advice, but the OP has my sympathy.