There are no specific device recommendations. Only general specifications.
This is what Jagex suggests: https://support.runescape.com/hc/en-gb/articles/360001313349
Personally, I think that's too low for playable performance, though I'm sure the game would run with that. I think I'd want to see double the memory, a decent mid-i5 processor and a GTX1060 or equivalent. That would see a decent performance.
That said, what's wrong with your laptop now? What makes you write it off?
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Wait for ryzen5 3500u Picasso, it is launched with 8gb dual channel ram and 256gb ssd
Alternatively ryzen5 2500u with similar spec is quite cheap It can cost as low as 500usd I own one with that spec and it run quite hot even when it is idle I have never played nxt on that laptop because I no longer play runescape, i dont even want to install the game client
Intel laptop is quite expensive recently because of the shortage in intel 14nm fab supply Amd igpu is theoretically more powerful than intel gt2