That’s pretty much my worry. I would be fine if they e.g. release their “official” lutris script or something, because at least then I would trust that they might be willing to fix issues if something comes up. But now that they are pretty much saying that they won’t support Linux in any way, but you might try these solutions on your own risk, it doesn’t really make me want to use them.
Mod Ash mentioned it on Twitter: https://twitter.com/JagexAsh/status/1701861633532792883
Mod Korpz tells me it’s built from tech licensed from another company. Inserting Linux support into it is apparently a considerably bigger ask than it sounds :(
I don’t have a Steam Deck so I can’t really help you with that, but I still find it funny that Jagex somehow decided to make a security improving Jagex Launcher for a multiplatform game, but then the launcher doesn’t support Linux and the method they suggest doing is running some random Lutris script from a random github repository which doesn’t have any kind of support from Jagex’s side. Apparently they can’t even get it to Linux because they are using some kind of a licensed tech that doesn’t support Linux at all.
I have one SSD which I use as a data drive between both Linux and Windows. I used to run Steam games from it, but there were some small problems sometimes, so nowadays I just use it as a storage.
Generally it works just fine, but sometimes Windows does something weird with it especially when running updates, so that Linux can’t mount it. During those times I just have to boot to Windows desktop and then come back to Linux and it usually mounts again. If you totally get rid of Windows, I don’t think this will happen to you though.