Unless Nintendo starts publishing their games on PC, I don't really see handheld PC's making much of a dent on the Switch's successor. The sales of Nintendo's first-party games on Switch show that's the case. Gamers, casual or hardcore, buy Nintendo hardware to play Nintendo games.
It's important to note that Nintendo ISN'T partnering with Denuvo. Denuvo is doing this in order to license it to other publishers.