Definitely not next gen seeing as how they leaked specs have them at xbox one level 1.3 tflops in handheld mode. you arent getting those visuals on an xbox one.
probably 10 tflops like the ps5, but you arent getting 10 tflops in a handheld until they get to 1nm AND when it gets affordable enough for Nintendo to put it in a cheap $300 handheld. so even if we get to 1nm in the next 10 years, we arent going to have nintendo get there for another 20 years.
Even then 10 tflops might not be enough. Look at Ratchet, the mario movie shits on it. Then again Insomniac targeted native 4k 40-50 fps so they wasted a lot of horsepower there. you have to wonder if Nintendo devs are also stupid enough to waste half the gpu on rendering native 4k instead of rendering it at 2k or close to 1080p like most CG is rendered at.