Is it safe to be inactive for too long while in a game on my Series S?

Yeah it's fine. I try to play while working sometimes and end up having to leave my console inactive for long periods of time and nothing has happened. There are settings to turn off the console after an amount of time as well.

I wouldn't consider anything that does not offer 4k @ 60fps (Or 4k ((Upscaled) @ 120fps) to even be next/current-gen. We've been living in a 30fps world for far too long. Upgrades we're promised and while many games aren't optimized perfectly (and, lets be honest "Series X/S Optimized" really just means "we upgraded it for the Series X capabilities and just assumed it would be fine on the Series S") better performance should be expected.

Sorry for the newb question: isn't saved game data backed up to the cloud or is that something I'd have done in settings?

Also, this won't erase my eternal drive too will it?

Well, In my case all games for one and series S/X are safe automatically in cloud, the games for Xbox 360 and classic, I don’t know if they're safe in cloud too or only in drive.

All your information in drive will be erased, games, local saves(have a copy in cloud) and settings.

So so long as I long into the Xbox Series S/X with my account, the one I use to buy the game, I download the game onto the console? I’m just making sure because the Xbox series S belongs to somebody else in my house hold, but I’m still able to use it even though it’s not mine. I was just trying to see if I logged into the series S with my account I could just download the game on there and then play it from there.

When it's not all laggy, pixeled and choppy; it has one major flaw. It kicks you out if you're inactive for too long. Not too good if you got further in a game and couldn't save.